I have a 468, 4.185 x 4.25 BPE swinging assembly runs great, small set of W9's pump gas motor, Torque monster. Working on a 471, 4.200 x 4.250 with a good set of W8's. I think you could go 4.25 x 4.5 510cid, the rod ratio would suck but you could do it, just my option.