The seats never changed. It was the seat tracks. The change occured either in the second half of 74 production, or early in 75 production. I don't think there are any 75s without a cat hump... I do know there are 74s without the hump, and I think some 74s have it. Anyway, 72 LDO seats, for example, are used into the 'cat hump' years. Only the tracks change. You can take the tracks off and bolt them to just about anything...