http://www.boomslang.us/obd0to1.htm
Thats what you need. You never swap engine harnesses, you just modify the one that came with your car. If you did swap your harness when you put in the z6, swap it back.
You don't need to run the p28 if your not running the z6 head and distributor. The bottom end is basically the same block, its the heads that make the difference between the two engines.
Check your codes and double check your timing, make sure you have it right.