Those 4.15 cranks use Mopar rod journals which need the block to be clearanced while the 2.2" BBC journals on the 4.25 crank usually just drop in.

As has been posted the 4.15 crank needs the short 1.112 CH piston with the long rod.

4.25" gives you 489-496 cubes using the 6.535 rod and the 1.320" CH piston.

No replacement for displacement and it's the same price.

Kevin