I'm looking into adding cartridges to a BMW R100GS fork. It's a 40mm tube with a 34mm (I think) ID so I'm looking for forks with cartridges that will fit. I assume the cartridge from nearly any 40mm fork would work but possibly if it's a USD fork the wall would be thinner, meaning greater tube ID and possibly a cartridge that's too big. Obviously I'll be doing some machining. So, if anyone has any relevant dimensions for this sort of stuff it would be helpful. I'm not looking to extend the travel so I don't need more than 225mm stroke, although I might run into overall length problems if they come from a bike with 300mm travel. So for instance, what is the cartridge OD and tube ID for a 4357 fork? How about for a Magnum 45? What other forks might have a good cartridge that will fit into the R100GS fork tubes? I'm thinking about a similar conversion for street forks also, but of course I'd be looking for even less travel.