Cable routing:

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CrissCrossFront by Dave The Golden Boy, on Flickr

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CrissCrossCables by Dave The Golden Boy, on Flickr

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IMG_0220 by Dave The Golden Boy, on Flickr

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UnderDownTube by Dave The Golden Boy, on Flickr

Hand made. A slick little leather cutting tool created the strips, and a rivet set completed the job. It wasn't all that difficult. I also salvaged and repurposed some toe strap hardware, making the leather straps with the same tool.
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I have one bike with bar-ends, a Velo Orange Polyvalent with Suntour Barcons shifting a triple crank with an 8 speed cassette, cables routed under the tape exiting at the stem:

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Overall I'm a pretty big fan. Sometimes I feel that the shift lever ergonomics aren't the best, especially since my front derailleur pull has a decent amount of resistance to it and the short levers don't give a lot of leverage. This is likely due to tight bends on cheap shift housing due to the under-the-bar routing, and maybe because I should clean and lube the FD. But to be honest, I only notice it shifting into the biggest chainring, and probably about 90% of my riding is done in the middle 40T ring.

The only complaint I have that is specific to my setup is that with the bars at the height that I want them, if the handlebars swing around the Barcons will hit the top tube - hence the handlebar tape wrapped around to protect it. Just be advised that if you like to run drop handlebars reasonably high, you might run into this problem.

I have been considering how I want to build up my 1981 Trek 716. My intitial intention was to set it up with modern Shimano or Sram integrated brake/shift levers, but I'm starting to lean towards the idea of getting some indexed bar-ends instead.

It would sure keep the cost down!

I agree with everything you said, in addition I will say that barcons are really versatile. I have used 7-10 speed drive trains with the same shifters. If I plan to do a tour that some how needs a different drivetrain all i need do is change ratios front or rear. I can even use different brands of derailleurs and still the barcons work. Currently I am going old school with a suntour rd, campy fd, 7 speed fw on a Phil wood hub. Rock solid and shifts great. Sorry the pic is non drive side.https://cimg3.ibsrv.net/gimg/bikefor...82bcaf8844.jpg

On the topic of barcons - I have Shimano barcons (not sure which model off hand) on my ~15 y.o. Rivendell Redwood. Until about a year ago I had them in friction mode, which worked fine. But then I started to experience "self shifting" when out of the saddle in a low gear, not great... I switched them over to index mode, which "solved" the problem.

From some reading I believe what's happening is the derailleur cable is slightly binding somewhere when the frame flexes, causing a sort of ratcheting action. I looked at where the cable routes under the BB shell and didn't see any obvious issues there, so not clear to me where the problem lies.

The bike is completely stripped down right now for a frame repair. When I put it back together I'll pay extra attention to the full length of rear derailleur cable and housings. But any hints on areas for special attention?

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Tommy Simpson with the Cannibal chomping down

And
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Patrick Sercu with Merckx

Cutting bars down slightly for bar ends was common practice. It depends on the bar. Some rando bars have shortish drops and seemingly are intended for bar ends.

I never like barcons myself. Too easy to bang my knees into them. Maybe I move around too much or something. Also, I have long ape arms and reaching DT shifters is really easy for me. I do have bar ends on my Clem bike with Albatross bars though. Perfect for that.

Even Eddy
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Man, that's an early pic ^^^.

He hadn't even swapped in Cinelli bar & stem and campy hubs yet.

As mentioned, trimming an inch off each end and using barends were popular for USA criteriums.

One slight improvement today is using them with modern Teflon lined stiff cable. Crispy 'friction' if such a description makes any sense.

And another pro, Manuel Fuente
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The great Gino Bartali
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If one is into classic weight weenie builds, a negative might be the weight of bar end shifters.

Currently in the build of a Teledyne alpine using early Shimano bar ends. With modern cables the mechanical action is precise though I'm tempted to rework them to reduce weight.

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Of course! You are faster than me. Fuente is in my avatar "showering" his Bianchi.

That's the method I see most often locally on drop bars, and what I tried recently with borrowed bar-ends on my bike's albatross bar. I just slit an old beat up set of foam grips to accommodate the shifter cable from the bar-ends while I tried 'em. Worked great. Cable wasn't in the way, didn't bind on slow, tight turns.

Worked well enough I bought some 25' or 50' rolls of cable housing and extra cables to experiment with while I settle on a routing method. I'm gonna try a full bar tape wrap next, and swap stems from the original dirt stem with built in cable hanger to a road stem and accessory cable hanger below the stem. Should make it easier to adjust the stem height without needing to re-adjust my cantilever front brake.

And no knee problems with albatross bars -- they flare out enough, and my bike has a fairly long top tube so there's plenty of clearance. If I put bar-ends on a drop bar I'd probably go for Salsa chowchipper or similar flared drops.