That shock info was just exactly what I was looking for! Not good news mind, I'm not getting any thinner in my old age. I'll need to get searching for a heavy spring.
Most of the racing I do these days is with the Twinshock Scrambles Club in Scotland.
They organise various national championships for older bikes & riders. I ride in the over 50s which allows me to ride a pre 1990 "evo" model and for that I restored a Maico 500 1986
However I've been trying to get an entry to the annual Vets MX des Nations event at Farleigh Castle (Chuck Sun, Mike Bell, Ryan Hughes, Doug Dubach, Jeff Ward and Ron Lechien all made the trip across this year) and also want to do selected National Twinshock Championship events, especially at Hawkstone Park. This is an English based championship and their rules mean I need to ride a twinshock machine.
TWINSHOCK. ANY BIKE MANUFACTURED WITH TWO REAR SHOCK ABSORBERS AND WITH DRUM BRAKES AND AIR COOLED INCLUDING UPTO 1984 HUSQVARNAS, PRE 82 MONOSHOCK YAMAHAS AND WATER COOLED ORIGINALS THAT WERE MANUFACTURED PRE 1982. FORKS MUST NOT BE OF GREATER DIAMETER THAN 46MM.
So a couple of weeks ago I bought a Yamaha YZ465 imported from California with a view to restoring and racing it in these twinshock events. I have it all stripped down and it is in pretty good shape. The exhaust and the suspension need some work, but not too bad and the rest is just tidying up.