LT1 engine swap-going from manual to 4L60E tranny?

I recently bought an LT1 out of a 97 Firebird. The engine came with all the accessories, pcm, and the entire engine harness. I am about to install this into my 95 chevy C1500 2wd extended cab pickup. My truck has a stock 305 with a 4L60E tranny. What I didn't realize is that there is a clutch on the back of the LT1, meaning the harness doesn't have the big gray plug equipped for my automatic tranny. How can I make my 4L60E work? Can I take the cut the gray plug out of my current engine harness and splice it into the LT1's harness? I assume the plug connects to the shift solonoids and makes the transmission shift. Any help is greatly appreciated, including having to go with a non-electric turbo 400. Thanks guys.