With a cheap Harbor Freight digital scale weigh one of the 383 rod/piston/ring/bearing assys' and one of the 400 ring/piston/ring/bearing assys' & post the difference. For the bobweight amt on each journal (4) the reciprocating weight of 1 assy's is used as is plus the rotating weight of 1 assy is doubled then add both sums up but in effect each assy should be the same (or close), for a start post what you get just as if 2 sacks of money contain the same # of pennies and the same # of nickels they will weigh the same. Unless someone has a definitive ans I'd wanna know now (one way or the other) rather than later (& maybe have to start over)