Basics-500 HP at the wheels with an auto trans is approx. 625 at the crank. Make sure everyone is talking wheels or crank to be consistant. For 350 cubic inches to produce 600plus HP is not an simple rebuild nor a mileage master. An Ls1 w/huffer is cubic dollars. As far as a drop in, stroking the existing 350 with good parts all around is the most realistic path IMO.