there is a differance in the bolt pattern from a 68 to 69 water pump. Needles to say you cant put a 68 water pump on a 69 motor. The timing chain covers are differant. As far as the length of the shaft on the water pump you want one for a 69 firebird 400. Its shorter than the one on your motor. Your motor came out of a 69 GTO? I have a casting date 1968 400. It came out of a 69 GTO and I had the same problem. Hope this helps Joe