I see this post is a month old and probably already resolved, but since I noticed the date after I typed out all the following...
Self tapping screws would cross-thread in a nut made for a machine screw.
Originally Posted by GoldDigger
OP, if the fixtures were old enough to be replaced in the first place, then they very well be on the verge of needing new ballasts anyway, even if the 277V ones work on 120V. It's not like 4 bulb 120 - 277V ballasts are expensive anyway:
Electricians do it until it Hertz!