Without knowing the internal parts used in each, you can't make any comparison at that point....you could be comparing a cast crank, hyper piston, Sportsman I-beam 383 SBC with a lightweight forged crank, Race rods, and forged pistons 427 SBC. Thus the difference in cost.From a popular,
reliable builder,
383/510 Dart. $7395
427/628 Dart. $10225
Did you do the math ?