My bad on the washer. You are perfectly right on the spacer on the clutch bell (on X it is 86121, XSS 86171) - Manual page 29. Regarding the slipper clutch. Completely tight is when the spring is totally compressed, then 1/4 turn back. If you tighten the slipper too much you don't have a weak point there and with ramps and jumps the excess reverse forces will be transferred to the next weakest point (the clutch, diffs, gearbox or spur gear/clutch bell). The slipper is a managed weak point so I wouldn't suggest tightening it all the way. Some others won't agree with me on that one, but decide for yourself what will work for you. I understand that the diffs has been pre-assembled and was just trying to eliminate small common mistakes (I made some of them myself). Now I'm starting to think the grub screw (86094) is missing on the cup joint (86272) as the front wheels do turn the gearbox (and therefore the spur) and it is a solid axle between the front cup joint and rear cup joint (Check page 51 of manual). The reason the car doesn't want to run with the engine in place is because the clutch bell doesn't rotate freely.

Sorry if I misunderstood your first post, I was in a rush out of the house when I saw it and made a quick reply.