[b]1981 RM 125 What part(s) are interchangeable year to year??[/b]

1981 RM 125 What part(s) are interchangeable year to year??

I already started another thread asking how big can the RM 125 be bored out too. That was before I really started taking my bike apart and looking at what I had. I was never a fan of off-road I'm an asphalt junkie. But while looking through Craiglist for parts for my Mini-Tard I stumbled on a "RM 125 not running and well used but not a total P.O.S." The description was accurate and for $100 I was willing to take a chance. If you ask me about road race bikes I can probably answer you but I'm stumbling around in the dark with off-road. My Mini-Tard is a PW 80 which has never seen a lick of dirt since I rebuilt it. Now that was a P.O.S. when I bought it. I actually toyed with the idea of snatching the 125cc out and putting it in a Mid Bike. But the more I read the more I realized just what I had. A small piece of history and I'm a sucker for nostalgia when it comes to bikes. So I decided to rebuild my little headcase and see what I could do. I don't care for a 100 point restoration I just want a cool looking vinny. After looking through Ebay I realized it will be easier and better to rebuild with as many NOS parts as I can but they list them almost strictly by year. Which doesn't tell me if a 1983 head will fit on a 1981 or if I found a 1982 aluminum piece someone found in a go-fast bin that was made to replace a steel piece...will it work with my 1981 or was it a piece that will only fit that year? Will a 1995 rear shock fit? All these are not just great for rebuilding they're just plain cool to know.