XR200R Upgrade to Vintage?

As some of you may know, the XR200s from recent years, such as my 2001, have forks and a spring that are really only capable of supporting somebody around say...120 pounds max? I have tried every procedure to stiffen them up with some good results, however I would still like to "beef them up" some more. So last weekend while at my cabin, I took the forks off my grandpa's 1982 XR200 and put them on my bike. That gave me an amazing extra 3 inches and a very smooth ride until one of the forks slid up in the clamps. Apparently the 1982 forks are ever so slightly thinner so my clamps won't hold them as tight. I was thinking of shimming them up with some tape or something to make up the difference however my dad disagrees and says that the tape will slip. My thought after that was to put a thin strip of coarse sand paper in the clamp to grip the tape, however he still disagrees. Please let me know if this is a plausible idea, or give me some other suggestions

I should also mention that I am looking into purchasing 1982 triple clamps as well as the forks but I would like to not have to go to the trouble of redoing my entire front end if I can avoid it.