40mm fork question

My question regards my 85 500xc, I have read in some of the threads that cutting the spring increases the spring rate, and you can cut the springs down to 24 inches and run a 4 inch spacer. Is this a good setup for this bike? Could I run a 4- 3/4" spacer to preload the spring a little? I just want to do the free mods until I can afford to get the gold valve. I also want to know if there are any damper rod tricks you guys do. I am about 230lbs sans gear, should I use 15 or 20 wt oil? I like my forks firm

Yes cutting some off the spring makes what is left stiffer. I would figure the bike was sprung for the guys you see in the picures in the owners manual. The problem is that the ends of the spring are formed a special way befor the heat treatment. I have replaced perhaps five inches of spring with pvc pipe for use on my Norton hillclimber and it works pretty well for the natural terrain type of ground but lacks for the jump type which is what is pretty close to all of them now. It weighs 333 pounds. I heated up the cut end and attempted to make it more like the cut off end but only could do so much and don't have a molten salt bucket to re quench the spring in. At least that is what I think they do before they temper them.

Some moto cross forks have pre losd adjusterss but they are for small fine tuning. No one really puts air in the air valve which would be preload. The idea is for say 12 inches of travel to have it settle .75 inch bike only, 4 inches bike and rider which really means different spring rate not preload. If you havn't already found it look here http://www.cafehusky.com/threads/vinduros-suspension-setup-recommendations.17836/

I weigh about 170 and use 5 wt or 7 wt oil but most likely ride different terrain. There is quite a bit more stuff inside an 1988 fork than the one you have. I can't really tell you the answer but I would ask would it be a better investment to buy used 1988 40 mm forks or the valves you are contemplating.