I bought this bike new back in 1990, and loved it dearly up until it started giving me knee pain while commuting. I've since bought a few other bikes, and was about to pass it on to my brother, thinking that it didn't fit me. Due to some parting anxiety, I made a last ditch effort to figure out if I could make it fit, and I think I might have it.

The frame is 18", which is fine for single track, but I would normally ride a 20" frame on the road. However, the top tube length is as long as my newer, better fitting bikes, and the quill stem can be raised a few inches. I can raise the saddle as high as I need to, yet I always had knee pain. Then, a lightbulb went off, and I measured the crank lengths on all my bikes. The bikes that fit have 170mm cranks, and this one has 180mm cranks. I never thought much about crank length until I started piecing together a bike on paper. I looked up a few calculators online, and consistently come up with 168.1 mm as my ideal crank length for 32.5" barefoot floor to sitbone. The result is that I believe I can make this bike fit me AND get it set up as a beast of burden for a very small investment in a new crank for my square taper BB.

So, I'm looking for feedback on two items:

1) Is it reasonable that changing from 180mm to 170mm could eliminate knee pain (specifically, inflamation from overuse of the tendon on the outside of my knee on upstroke)
2) The Sugino XD300 170mm is what I have my eye on. Right gearing, good rep, steel rings, $45. If I'm more of a spinner, would 165mm be better?

BTW- in addition to replies on the crank/sizing question, please feel free to hijack this thread with liberal doses of late 80's/early 90's ATB tour conversion photos and specs.