the reason most people are saying that going the blower route will be expensive is for 1 the blower is going to cost 2500+ to get it delivered. Then I would say that it would be a little dumb to run a blower on facotry heads (just my opinion) and I'm not sure those heads in the shape they are in can even support 650hp. So there is a set of aftermarket heads, 1800-2500. To do this he is looking at 5,000 easy, and that doesn't include the machine work to the pistons (i'd just buy new pistons).
Since this is a 427 BBC which is basically the same block as the 454 BBC just with a 396 crank, I would say go after building a 496, he'll have about 2500 into the rotating assy and the machine work. Then go after the aftermarket heads, and probably another cam. It isn't too hard to make 600-650hp out of a 496 (with the tq to match). Then later on if he decides he wants even more then he could toss a blower on it and be in the 750hp range (suposing the block and other parts hold up).