How hard can i rev?

You can Rev anything ole thing to 7,000 rpm at least once or maybe twice. :razz:

Depends on how soon you want to rebuild it I would think.

I'd stick with 6500 unless you know how well built the bottom end and your valve train is. specifically Oiling system, Bearings, Engine balance, Valve springs and Retainers. Stud kits a good start but there are a lot of other things needed for a dependable higher revving engine.