If you are going to go the conversion route, here are a couple of tips re what to look for in a frame:

Excellent fit (duh).

Horizontal dropouts (duh).

Commonly used dimensions in the bb shell --- to tweak chainline you will probably wind up swapping out the BB for one with a shorter/ longer spindle, and this way you can just get one over the counter at your LBS instead of scouring the internet for some farked up NOS Moldovian unit. Japanese, American and English bikes won't steer you too wrong, there are others too.

Cranks that will work with a cheapo square taper BB like the one you'll get to tweak chainline.

A working, non "notchy" headset---this will save you a little money.