283 piston would drop the pin 0.125", 400 rod would be 0.135" shorter, so yeah, you would be within 0.010" of being right. You could juggle the deck height and get there, if you had plans to deck the block anyway. You may not be aware that aftermarket pistons are way shorter than production units to allow for decking, so do some careful measuring before you lay down your money or the deck height could be off too far to get good squish on the motor.