I believe all of those wires can be located right at the old PCM. You can depin them from the connectors and then push them into your new PCM connectors and not have to cut the wires. Lextech sent me a file about installing a Gen III using the original vortec harness, and to get the tach functional you need to splice the white wires of the coil and ignition control module together. I would recommend you contact him to get the file, even if you're not going to use your stock harness.

There is no reason to use the stock computer, as the swap computer can handle all of the functions. Contact Lextech to get the 0411 PCM swap file as well, and use the information in there to get the A/C and ABS functions running from the 0411.