I did a 4.3 engine swap in a 96 Astro van. I used a block from a 91 Blazer and put heads and everything else from the 96 on the 91 block. I could not use oil pan or timing chain cover off the 96,wrong bolt pattern, so I used the oil pan and timing cover from the 91. Now I can not install crank sensor and engine will not start. What can I do to get this thing going? If anyone can help I would greatly appreciate it! Thank you! John