I note this is referenced in the '72 S driver's manual: "When replacing a worn belt make sure that the replacement bears the designation Phoenix-Rhombus DA 9.5 x 710."

However I believe these had a date code on them e.g. 6/05 would be May '66 but I don't know what would be the code for any particular month in 1971 (my car was built 10/71).

NOS preferred.

Please PM me if you have one.