It just doesn’t look correct. Was this ‘73 Raleigh Competition always like this? I’m tempted to close it up some.

I would close it up some, enough to fit cable housing, I would use a vise. Wood Beyond top tube, with a rod through the braze on and some shims to isolate and not dent the tube.

I'd use a c-clamp instead of the vise, gives you better control but otherwise pretty much what you said and go SLOW.

a Kant-Twist clamp…. Loaned out and never returned.

If it's divine...

I'd try fitting a correct diameter steel rod, anchored in the other guide and tie-wrapped in position and then tap tap tap with a lightweight peen hammer. Everything looks like a nail in my world.

Just because steel rods have been referenced twice, I'm going to elaborate on that and suggest using the correct sized drill bit from your index...

Yes, I would lightly tap

Why not just braze a new piece on , its already down to bare metal and in need of a paint job. With the right tools its a fairly easy job to remove and replace it.
Ive done quite a few modifications on frames and its very cheap and easy .

Doncha' just hate when that happens? If I had all the tools I'd loaned out and never saw again........

It is easy to over-think things and become lost in finding a solution. Stick a drill bit in the eye that is about the same diameter as the other good one on the frame which is larger diameter than the housing stop itself, and then tap it down with a hammer. The metal is soft and will conform very easily.

I didn’t think about possibly denting the top tube. Thanks to all for the suggestions on distributing those forces. I haven’t gotten to it yet as my hammer is preoccupied with a higher priority garden fence project.

I was taught when I was a pre-teen how to use many a tool by a master machinist that lived across the street from where I grew up. Later when I was about 16, he gifted me a set of hand tools wit the instruction to take care of them. My shop teachers also taught me to buy the best tools I could afford and that had lifetime guarantees. And all of these gentlemen told me to not loan tools or to ever sell tools as I can always make more money using them than I can selling them. Through the years, I've followed their advice and the only tools I've loaned were within the shop I was in or my hands came with them to make sure they were used correctly and not abused (my screwdrivers are not punches and chisels). I've handed some tools down to young men I've worked with often explaining that the tool is older than they are and giving the advice I received from others. But I still have never sold a tool and have not lost one due to loaning out.

I do tip my hat to those here that freely offer to loan something to someone not far removed from being an internet stranger. I just cannot bring myself to do that and have always neither a borrower or lender be.

For a guaranteed no-touch bend, Uri Gellar might still be available.
Seriously, if were my bike, I wouldn't clamp or vise for fear of damaging the tube; I'd adjust it with a brass - faced or similar hammer.
Replacing would be ideal, as suggested, and if within budget, maybe you can add on/correct any additional items!
Hammering and bending are frequently leaps of faith in my experience as a mechanic. On a slightly squashed cable guide on my own bike, I opted to iinternally file it to correct open diameter rather than try to bend it into shape.