short answer is no. What is the matter with the SM420? an SM465 is close, but you need a different bellhousing. The center hole in bellhousing is bigger for an SM465 (an 465 is about an inch longer so, you need to shorten your driveshaft.) Still a direct 4th gear though so, doesn't gain you much except a newer tranny. Also, shifter will be a bit farther back.
