The holes are a different size? Everything is pretty much identical between the 454 and 496. The 496 just has a stroker crank. Both are external balance and I don't think the balance changed, so the flywheels are probably the same. If not, just buy the flywheel from a newer truck that came with the 496. I see no reason for it not to work. The injection setup should be able to compensate. The new motor just going to pull a little more air at WOT.