I love this era of Trek. I have an '81 750 Pro that is one of my favorite bikes I've ever owned. Trek was all over the place back in those days using Campy, Shimano and Suntour. Sometimes mixing brands on the bike. Really most bikes back then didn't come with a "groupset". The '82 736 model came with SunTour Superb 6 speed, Cinelli stem and bars and Campanolo hubs. If you want to update the frame it should be fairly easy to cold set the rear to 130mm and put on a modern groupset and wheelset. My '81 Trek has 6400 Ultegra 8 speed brifters on it and it looks pretty good and works very well. Personally I would go the Suntour Superb route though it may be hard to find all the necessary bits.