On cost, If you have a decent 440 forged crank for a core and a competitive machinist, the 451 made from a 440 crank can be lower cost. Same comment on rods. If you have a good set of standard dimension 440 rods, that favors the 451. The 470 uses a chevy style rod. If you are buying all new, there's little if any cost difference.

They are both good... it comes down to matching heads and picking your power curve. The 451 will want to wind higher than the 470 other things equal.