When (year) was the 8.5 first used in a GM car? And what car/model was it? And only had leaf springs or mono springs. Rear in question 10 bolt 8.5 posi,w/ leaf spring perchs, does not have complete numbers on the tube. Drum to drum 61-1/2" +, axle tube to axle tube 55-1/4" , centerline perch to perch 45 1/4", date L112= Dec 11 1972. Could it be a 2nd gen camaro rear? thanks