A 4" 8-32 SHCS with loctite is sounding simpler and might be stronger than either solution above. (At least after thinking about how well I'd execute the operations.) Since the only true constraint is the size, #8 and 4" long, if I have to replace the existing screws, think I'd go with 8-32's. Otherwise I'd have to go with a custom screw. This motor isn't worth having a custom screw made. Probably good enough to simply use some Grade 8 8-32 threaded rod and some nuts.