You might first measure the distance between the rear dropouts to determine whether the distance is about 120mm or 126mm. If the bike was originally a 10 speed with a five speed rear cluster the distance will be close to 120mm. If the bike was originally a 12 speed or more the distance should be near 126mm. A distance of 130mm or more indicates a modern bike that uses freehubs and rear gear clusters rather than screw on freewheels. After you know that you can locate a rear wheel/hub combination that is the correct width to fit between the dropouts. If you want the bike to have index shifting you have to acquire index shift levers with the correct number of detents (probably 6) and a derailleur that is capable of index shifting that will work with the shift levers. Index shifting came about around 1987. You cannot normally mix Suntour and Shimano derailleurs as the cable pull differs. Shimano 6 speed systems (levers and derailleurs) are often on e-bay. I'm patial to the 105. You will need to find a rear wheel that is made for screw on freewheels. Not so easy these days. Freewheels are currently available from Nashbar, Shimano, and a small company called IRC. I have been pleased with the Shimano units but not the others. The wheels and hubs will be your biggest challenge to locate because wheels are more susceptible to being damaged than any other part on a bike. Next susceptible is the rear derailleur. brasel