This is a 1977 Le Tour II, with a 28.6mm seat tube. There is no screwhole to mount an under-BB cable guide, and I'm not prepared to drill & tap one.
Now that I'm looking at it, I think I can fit one of those DT cable guides (with a housing stop on the left and an angled guide on the right) and Dremel off the RD guide. Clearance shouldn't be an issue, since I can mount the guide at least a couple inches below the FD clamp.
That's a lot of cabling, pastorbob.