128 mm spacing wasn't unusual around 1990. When D/A was 8 speed and 130 mm, and everything else was 7 speed and 126, it saved having to make 2 different frames. I'm not aware of it ever being a problem.
If it bugs the heck outta ya, and if you can machine the dropout blocks straight and flat, I can't see why it wouldn't work, but I wouldn't bother. Stick a wheel in there and ride it like you stole it!
(And, let's honest here... ya kinda did... 200 bones is a sweet, sweet deal!)
--Shannon