I have a 92 454 with thunderbolt iv ignition. I have recently had the block bored and all new internals. I fired it up today and it sounds goog. I was trying to time it to 8 degrees bdc, but if I go any lower than 16 it starts to miss and backfires out the exhaust. What could cause this? I also cannot get it to fully engage in reverse, forward and neutral seem good but it grinds when put in reverse. If i put some tension on the shift "dog" it will stay engaged. I think that the cable needs adjustment put I have ever done this. Can anyone point me in the right direction?