[FWB]

so the counter weight isn't needed after you zero balance the 428 crank with the new reciprocating assembly, that was a factory setup. the chevy piston, is kind of a mislabeling, the pistons are probably for a 4.250 bore(chevy stock size)
so your motor if it is 4.250 x 3.98 stroke, i think it will end up being around 440 cu/in.
your bore could also be a overbore of the chevy size also, +.010, +.020....etc