Heh streetsweeper I have been working on these cars all my life 50+years and have never known of a taller gear for these cars some have said that the automatic chevys where a slitley higher ratio but I have no specs to prove or disprove it . Aside from that I know of no boltin replacement rearend I did however put a early Camero in a 51 but when going to a open driveline you must convert to a later trans which I fear will not match your bellhousing wich is the only one that will fit your 216 I allso instaled a 68 250 streat 6 with matching powerglide in that same car A lot of fabricating was required but that car is capable of 80 plus cruising speeds and air conditioning BUT I WOULD NOT DO it anymore . Please keep her just the way she is SHE LOOKS LIKE ONE SWEET RIDE "OLDSCHOOL"