Chain line is good, cable is brand new, and this pic shows big-big.

I thought of the hanger being out of alignment, but visually it looks good.
Without the tool I don't know how I'd check it more exactly, or tweak it.
You guys would probably frown if I suggested a crescent wrench!

Show a picture of big (F) small (R)

my lbs and manufacturers recommend small small. I find that doing small small gives me the max chain length which has been helpful when doing 52/39 and 11-28 combos with 7400 durace see

That looks good.

Thanks. At the risk of forumscorn I took a crescent wrench to the hanger and gave it some leverage. Not sure I gained much, if any, but thought it couldn't hurt.

The RD is now dropping down onto the 12 cog about half the time, better than before, but not right yet. When I re-assembled I double-checked my limits, and held pretty good tension on the cable, in the small cog, while tightening. It's still not jumping inward very successfully, so I'll also be working on that tomorrow.

I'm hoping it's my inexperience with brifters causing my woes, and that I'll figure it out eventually!

Chain length looks right to me. I think you're good.

You might want to play with your B screw adjustment, and see how that affects things. Usually I shoot for the RD cage to be a bit more parallel to the chainstay.

RE checking your hanger alignment without a tool, it can be done. I've always had a tool and but like I said earlier, you can do it with a rear wheel. Here's a video from RT:
I like to adjust the derailleurs without using brifters at all to start with. Yank on the cable by the downtube to shift.

Cool video, thanks for sharing it.
I'd be a bit nervous using a true wheel from one of my other bikes, though.
With the torque needed, I'd worry that the trueness of the levering wheel might be compromised.

Thanks to RJ for making it. (not 'RT') I've heard of him but haven't really watched any of his videos. This one popped up with a quick google search.

I can understand your worry about tweaking a wheel, but IME wheels are pretty strong and derailleur hangers are not difficult to bend. OTOH, he used an MTB wheel for this... If you're worried about it, you could always use a wheel as a gauge only.

Buy a derailleur hanger adjustment tool, or borrow one. If you were still in DTW you could borrow mine, I'd even do it for you. It's a one beer job.

There has to be a member close to you that has one.

Nice. If I were still in the Motor City I'd be all over your offer!
They probably haven't had one in a while, but I've always regretted leaving Detroit before experiencing a Slow Roll. Those were supposedly quite the weekly event!

I'll pull the rear wheel off my hybrid and check the alignment that way. It sure looks close, but that will at least let me know if it is perfect or not. I may even use the wheel to tweak it, but will be proceeding cautiously.

its surprising how far it can be off and look ok. I wouldnt worry about tweaking your wheel. It can handle it.

Make one. The bolt will be the biggest problem (10mm x 1.0). Boltdepot.com carries them. Drill press is recommended.

Dual-wheel method showed the hanger a bit off, which I believe I corrected.
I'll hunt around for the tool, but until then I'm ruling the hanger aligned.

But, the RD is still not dropping the chain onto the small cog, messing up all other smaller cog shifting. I even lengthened the cable housing entering the DR, to decrease friction, just in case that had any affect.

How's this for a possibility? The top jockey wheel is so close to the 12t cog that chain stiffness slows or prevents the final shift?

To be fair, none of my shifting woes were ever caused by the length of the chain. It was always hanger alignment, RD, or cables.

Shimano seems to think the same. For me the thing would def have to be cranked down quite a bit to clear the small cog better.

JMO of course but finding some Shimano instructions to read might be illuminating

So if you completely slack the cable*, and back out the limit screw all the way, the RD still won't shift into the 12t? Ignore the brifters completely, shift by pulling the cable and letting it go.

* (let out like a half inch)

Have you got the cble secured the proper way in the derailleur cable anchor bolt?

Cheers

Yes.

Correct. About the only time the chain drops all the way onto the 12 is if I'm manually shifting, ignoring the brifters, and letting it drop from midway up the cassette. Drop-clicking one at a time, it stalls out on the 13 cog.

I'm liking my diagnosis of the jockey wheel being too close to the small cog, but don't know how to widen that distance. I'm not sure the B-limit screw would alter it that much...

I believe that the type of derailer housing is the problem here.

This is the old, very stiff 5mm housing that prevents the rear derailer from floating about the cassette properly under it's dual-sprung movement. No bueno.

If the housing were longer it would be less of a problem, but this derailer is from the 4mm housing era and needs more flexibility there.

By the way, did you perhaps use any grease on the cable? What you want for best shifting and strong return action toward the smallest cog is some original pre-lubricated SP-41 housing, 4mm in diameter and of sufficient length for the guide pulley to track the cassette profile.
And the cable guide at the bottom bracket should be plastic, or with plastic noodle at least guiding the cable there.

The 9s-era derailers used modest return-spring tension that relied on free cable movement along the entire path of the cable.

Can you post another image taken from the rear of the bike and looking towards the front? The one you posted earlier is too small to make out details.

Cheers

The B screw shouldn't need to be super optimized just for the RD to drop the chain into the smallest cog. Assuming the hanger is now close enough to aligned, that really only leaves friction issues. This could be isolated by disconnecting the RD from the cable completely. Shift it into the 13 by moving the parallelogram with manually, ie with your hand, and then let it go. If it drops right into the 12, then you have a hang up along your cable somewhere. If it still won't drop in, there's not much left except a still bent hanger, stiff pivots, or a weak spring in the derailleur. Maybe a tweaked jockey cage. I'd make sure your cable is moving smoothly first.

Personally I advocate plenty of grease. No cable has not moved because it had too much grease. However, if you are using high tech prelubed cables, along with the correct matching housing, you don't need too. OT but this was a big religious debate when lined housing first came out.

Also make sure any linings are properly opened up with an awl, and housing ends are ground smooth.

I bet this is the problem!
Although the cable is greased, the housing is definitely old, and stiff.
(The cable guide on the BB is plastic, and I even have that lightly greased as well.)

YES!
I've operated the RD without being connected to the cable, and it drops down fine.
I also open up housing ends with an awl, and file them smooth.
I'll be shopping for some modern and appropriate shift housing, and keeping my fingers crossed that this will solve my woe.

salamandrine, and dddd, thank you so much for sticking with me while figuring this out.
Also, of course, others who have chimed in with opinions and advice.
I shudder to think where I'd be without the help of this forum!

THANKS AGAIN!