This should work on any custom project if you are thinking of doing a mono shock conversion.
My bike is converted to an enduro rear swing arm and 80s style dirt bike mono shock. The shock was to soft and would completely bottom out from accelerating hard. I looked around everywhere and could not find replacement shock springs or info in the dirt bike world.
The best info I could find suggested the shock had about a 150lb spring on it. I was looking at one of the car parts catalogs I get in the mail and I hit the jack pot. The replacement springs for aftermarket coil over car shocks come in just the right size and any spring rate you want 100-650lbs. And they are cheap enough that if you don't get the feel you want you can just try a different spring rate (~$40)
I bought a 10" 375lb spring with the correct 2.5" ID. It fit great. It is just a little on the stiff side, but I wanted to be able to ride a passenger.
I didn't revalve it or anything, just changed the spring. It is not bouncy or anything. I've had people tell me this could blow the shock or have all kinds of bounce, but I have no bounce and we aren't talking about doing motocross jumps with it. I have several hundred miles on it so far with no problems. Speedway has a huge selection of all different sizes and spring rates.
http://www.speedwaymotors.com/Shop/Coil ... meter:2.50