1979 was the transition year. Many 1979 parts are unique to that frame. From '78 down, your good to go as pretty much every part has been reproduced. Hell, there's still NOS stuff floating around. From '80 up, parts should be easy enough to find as well. If I decided that back surgery was something I wanted in the near future, I would hardtail a 78 or older model. But that's just my preference. Never loose sight of the reality of antique Ironhead Sportsters. Though they are really cool, they require enormous maintenence and upkeep. At best they are a collection of parts that "almost" fit together. Evo anything will be infinitely more reliable, but inversely less cool. The people who ride, and I mean actually ride Ironheads, do so out of a true love and passion for them. Not cause they need a cheap way to get to work. Good luck with whatever you decide!