A500 or 727 with GV?

How much beefing would the 518 need you think to handle 400-500 hp? I don't really feel confident yet in doing my own rebuild, I'm currently in school for this stuff, but I'm not there yet. So I would be taking it to a shop for the rebuilt which I was quoted about 1k. Does the Bellhousing bolts line up on the 518 to a 360 motor?

Thanks,
Mark