The Model 10 with SN D343339 was shipped in 1971-72. The Model 36 SN you list, 9J1341, doesn’t look right. Generally the J would be first and numbers following. Could you maybe have the wrong order and the SN should be J91341? If so, the the ship date would be 1969-70. The other possibility is you may be reading an assembly code. The serial number should be on the bottom of the frame. Some pics of where you got your serial number, the inside of the crane numbers and the bottom of the frame may help.