Looking for overdrive trani advice for /6, please help

Yes, I have the Clifford headers, dual exhaust. (the exhaust system has an annoyingly loud, howl between 45 and 60 mph) I bought the car about six years ago and the odometer said 97000 and was disconnected. There was not much of any history given to me about the vehicle. Its burning a little oil, leeks a little oil from the oil pan and needs a motor mount badly all of which, I have been told, can only be repaired by by pulling the engine. Nothing else has really been done to the engine except that I also have a complete supersix set-up sitting in a large box in my garage from a 1978 donar car waiting for?? I have heard mixed reviews from many people here about whether I should keep the Clifford or go for the SuperSix. I'm not anywhere near the league you mechanics are in but I'm dying to learn! I do not have that much money to work with which is why I'm going slow AND asking you guys for help so that I don't have to do this twice. Thank you Slantsixdan!!