I think the balancer and flywheel/flexplate 'have' to be 400's.And the rodbolts will hit the cam and block without mod's.You can get 383 cranks for under $200(cast).There are various rod lengths to use but I think most use the 5.65" rod.You can get the rotating assembly's for around $600 at several different places.This is about the lowest cost motor to build $/hp and a good one too.
There are many 383 guys on here,,,,where you at guys,,,???