My estimate of 600 hp came from a friends combo that is a touch different, but low compression. The Fast and Furious, Joe Schmall that races locally in the tri state area runs a 446 cube RB, box stock small port Eddys, flat tops about .040 in the hole, 590 cam ,850 Holley, single plane, and a well sorted chassis combo has run 10.90s in great air at 3900 lbs! Shift point is 6200 rpm. The low deck would have some advantages to offset the 17 cube difference I would think. Basically I believe it is just how much cam you are willing to put in the motor, and spinning it up to maybe 6500. Chamfering the bores for intake valve unshrouding would more than likely help, as that was done on 426 SS motors If I recall correctly. Again, good head porting, and a roller ought to really make some steam.