For Sale: Koga-Miyata RecordPro 'rolling chassis', Lo Pro

Tempted to build this "period correct", but I'd need to get the shifter bosses repositioned if I went that route, so I'll probably move the DA cranks and rear wheel over to this from my Fuji and run it fixed.

Sorry, I really don't understand what the problem is.

If you are going to fix it, you can leave the shifter bosses as/where they are. Even better: cover them, so you're not going to injure your legs when standing on the pedals or so.
If you wanna ride with down tube shifers: you have the perfect bosses in the right place.
With any other shifting mechanism, you can put the with the ST-7400 brifters enclosed cable adjusters on the shifter bosses.
I'm afraid I just didn't get your point.