AND yes your 390 crank will fit in the 360 using the rods and pistons you have if you bought 390 pistons originally. I doubt that using the 360 crank will give you much compression because of the pin placement on the 390 pistons. Compression distance piston pin to top of piston: 360 (1.825) 390 (1.775) At least that's what my book lists.