318 0r 360

The rear end should hold up as long as he isn't just killing on it every time he starts the car. I used a 904 trans behind a well build 360 and as far as I know it is still going strong. Depending on what you have I would look at using a 318 just because there are so many more of them out there. There are 390 stroker kits for them if you wanted to pull more out of one. As far as the suspension goes I used the /6 torsion bars and stock suspension with the 360/904 set up that I had in my Duster. Worked great. I drove this car everyday. I don't see any problems with what you are looking at doing. Very realistic.