If you can get a 5.3 for that cheap you should go that route. Your not likely to do a 3.4 swap for that. You could always sell your toyota cases and go full size stuff. I think someone makes a doubler to put a dana 300 on the back of whatever t-case comes with a th350, 203 or 205 maybe I'm not really a chevy guy. A 300 will allow you front and rear disco and you can get a super stout output for it. I will go the dana 300 rout if I can't keep my rear toyota case together.