Redrilled rear axles

I just picked up a very nice/clean set of a body 8 3/4 rear axles that have been redrilled and 3" studs. The question is that the oringal stud holes are not filled in, do I need to have the filled or are the ok to use with out filling? :scratch:
The guy I got them from said he ran them with 500HP with no problems, he finially went to a narrowed rearend, and I bought them for $100.00.
Also how much HP do you think they can handle?