I would drop the gtp engine into your car, make sure it runs and shifts good, sell the other tranny, and sell your orig engine. Part out the gtp that was t boned to the max, scrap. You may come our ahead.
The plan has changed but I'm dropping the 98 L67 motor and trans into my 99. Selling the L36 for 200 and parting out the t boned gtp. The plan is to come out ahead but new fluids and new gaskets are expensive.