I don't know of a manual, but if the shock is anything like the one which was on my 85 IT200, and I think it is, then I can help with some how to. I had mine apart once. It's quite a bit different to dissasemble than a modern shock.
Let's start with some basics, just so we're on the same page- Is your 83 a linkage suspension or the old triangle frame? And, does it have the rebound adjuster knob down on the eye end? Last, does it have a remote resivour?
------------------
-01 RM250 (mine) & 01 RM125 (kid's)
-Senior A Enduro and Hare Scramble Rider.
"Yep, that 14 yr old A Class rider is MY kid; He learned to ride from ME!!"