Also on the 383 combo, check to see how much clearancing was done on from EACH rod-to-block ....?
If they used stock rod bolt type rods and had to grind a bunch off the caps to clear the cam, or had to clearance a lot at the bottom of certain cylinders because of a bad 'centerline offset' from a bad mold pour, skip the 383 and go for the 406...
Just my honest opinion...