Need Some Engine Help

[PKRWUD]

I can't help much, but I'll share what I know. Except for the CJ 428 and the SCJ 428, 428 heads are the same as 390 heads. The 390 and 428 blocks are pretty much the same (except for the bore), and the rods are the same. Swapping a 428 crank into a 390 would work with either set of rods, but would require special pistons, depending on how far you overbore the 390. If you took it to 4.130", you could use any 428 pistons you wanted to, to obtain the desired compression. The one thing you have to remember is that the 428 crank is externally balanced. You need to keep the 428 balancer and flywheel together with the 428 crank, and have them balanced together.

Hope this helps.

Take care,
-Chris