Chevy Small Block engines have used three different timing pointerlocations. Pre '69 engines have the TDC mark 2° to the left of the keywaycenterline. The '69 to '85 dampers have the TDC mark 10° to the left of thekeyway centerline. The 1986 to 1991/1992 have the TDC mark 40° to the leftof the keyway centerline. All of our SB Chevy dampers, as well as all otheraftermarket dampers, use the 10° TDC position. Our 6.75" diameter modelshave two TDC marks, one that is 10° and one that is 40° to the left of thekeyway. If you have a pre '69 vehicle you can use one of the aftermarket bolt-ontiming pointers to align correctly with the timing marks on our dampers.