Hi Chris c.
The r200 in the 77280z can handle 400 - 650HP. The chassis however can not handle at all this amount of power without serious frame bracing and weld work. Were I thinking of a 600+ HP 77Z then first to happen would be the differential getting welded . BTW, I run a ' Detroit Locker ' differential in my 77 road car. It handles 320HP easily from my L28. You can still find these 'Detroit Lockers' for prices beginning about $500.oo. Have fun. shane-