I would tend to think it would be pretty hard to get 600 - 650hp out of a stock stroke street hemi while still being streetable and able to run on pump swill. A factory race hemi grossed out in the 550ish range with headers IIRC.
I think your friend needs to;
- pony up and stroke it - give up being streetable and pump gas friendly or - lower hp expectations to something more reasonable; maybe 500 - 550hp
