Be aware that the Indy SL carts will only fit the Indy SL forks as the stanchions are a smaller diameter than the Indy C and XC. Basically (at least for the Indys) you remove the elastomers and the top caps and these just screw down in place of them. Then pump them up. I think the Judy ones fit the same way. It really is that simple.
The other sockets and pins and such are there in case you want to alter the damping. This requires you to dismantle the cart but I'm not entirely sure on the exact procedure.
MRP now own Englund but the carts are now out of production.