Converting my '77 TX900 to FG in the early '90's was a doddle, it's been in service since including LD/FG riding.
To me a quality road FG frameset needs to be light, compliant, lively and equally poised standing to power up grades and spinning down them on rough secondary roads. With no ability to coast and ease out of the saddle over bad surfaces a FG machine and the rider take more of a beating than FW bikes, ride quality and neutral predictable handling are something to consider on a FG machine ridden for distance.

edit: 3mm spacers on a 126 & good to go if the axle is long enough.

You have lots of choices, enjoy.

-Bandera