Thanks, dan--I remember now; A spacer was needed to go from a 3.73 to a 4.11 or lower gear until the aftermarket came out with the thicker ring gears. Zoom sold a lot of the spacer plates in the late '60s and early '70s! lol On the street factory Eaton 4-Series carriers were pretty rare, and everybody was running 4.11s or 4.56s--some hardcore guys even ran 4.88s and 5.13s. I ran 4.88s in my '64 Impala for awhile, but back then gas was only 32 cents a gallon. Oh, those were the days!