here is your price difference between building a 454 vs a 496/489 (.030).
4.250 (496 crank)
4.00 (454 crank)
they both use 6.135" rods so there is no price difference there, and you will have to buy a set of pistons that have a shorter compression height, but like when buying 383 pistons over 350 pistons there is normally next to no cost difference between the two.
if you are going to have this built then i guess you could go with the 496/489, it is a little overkill as the 454 can make gobs of tq but just like people like to build 383's instead of 350's, i can understand it cause there is a minimal cost differecne between building the two.