The idea of a 6 speed Uniglide hub is good. I’d go a bit farther and find a 7 speed Uniglide/Hyperglide freehub body with a thin flange and mount it to a deep flange hub. I’ve done this with a Hyperglide body and a shim and didn’t have an issue with the hub bevel. You should pick up a couple mm’s in freehub body width.
With that, I’d just run a 2x4 (44-28 with 13-34) spaced to 5 or 6 speed with and use friction shifters. I’d center it to get the best chainline.
The caveat is longer rear derailleur limit screws and how tight you can set the high-low.
John