If you really want to build a 383, and don't have any of the parts, you'd be wise to just buy a complete balanced rotating assembly. There's no need to bother trying to find an original 400 crank as there are several brands on the aftermarket that already have the correct diameter mains. The rotating assembly will come with the correct rods and pistons, damper and flywheel/flexplate already balanced. You'll still need to do the prep work on the block, but at least you'll know that the rotating/reciprocating parts are all compatible.

Bob