I used these, http://carshop.carshopinc.com/produc...id/74328/LS1GM, but now there are a lot more available. These are gaining in popularity, http://dirtydingo.com/store/Dirty-Di...323/index.html
Or look here, lots more. google search ls1 engine adapters
Also, just go ahead and run the 60e or 80e it'll just make things easier.
Call them for your harness and pcm tuning. http://www.nelsonperformance.com/