1996 Nissan Maxima Car could not go above 55 with out shaki

I bought a 1996 Nissan maxima Gle from this guy. When I bought it he told me it needed a new rear shock-strut and beacuse of this he didnt want me to go on the highway. So I test drove it though the city and it drove fine. Seemed slightly loose but nothing too crazy. I bought a new rear strut and he was correct the old one was junk and now I think I have fixed the problem. Cant test drive the car because I have it torn down and Im preping for paint. Well it hit me the other day, now that its all torn apart, that what if that wasnt not the problem? What if I paint the dam thing and go to drive it down the road and it shakes all over? The reason for my consern is, When you lift the car up to put it onto four jack stands, Im lifting one side at a time and everytime the rear passanger side is about an inch or 2 higher then the other three lift points. And it just so happens that that same side was also involved in a rear/side colision before I bought it. The body work is all complete now but my question is could the sub-frame or the body of the car be twisted? I have another rear end in another parts car I own so I could swap the rear out if the sub-frame is bad but could it be the middle of the car, the body in between the sub frames that is twisted? If thats the case and I need to have it straightened then the time I just spent aligning body panels is wasted because when a frame shop twists it back it will probley mess everything up. PLEASE HELP ME! ANY FEED BACK IS WELCOME. Thank you