Ls1 Wiring?

I am doing a LS1 conversion on my '70 Gremlin, anyone out there know how to go about getting or converting the original wiring harness? SUMMIT's got them for $1500, but I want to try using an original harness and get the computer re-flashed. I just got back from the junk yard and almost had everything taken off but the wiring go into the fuse panel was confusing.

What are you guys doing for the engine control system?

I bought a book of wiring diagrams and instruction on how to build your own harness for the LS1 off of ebay for $30. Pretty good stuff. If you can't find it let me know and I'll copy mine and send it to you for a small fee.

Where and how much is a re-flash of the ECM going to cost me?