I slacken the undertray to lower rear engine fixings and remove the undertray rear bolts. Let the undertray swing down and you should be able to fit the gearbox / clutch assembly. Adjust it towards the engine so that you will have max clearance at rear when you swing it up. swing it up and put a cheap car scissor jack under the rear of the undertray to hold final position while you put in bolts. Fit primary chain. Nip up only the gearbox clamping screws. Adjust the chain by pulling the box rearwards till primary chain is a little too tight. Tighten gearbox bolts a little more but not completely tight. Final adjust primary chain by using adjuster to push gearbox towards engine. this ensures that the adjuster is in hard contact to stop gearbox moving rearwards within the clearance in the system. Be sure to rotate the engine and try chain in several positions as there is invariably loose and tight spots. Set to half inch free play at tightest position. Lock up gearbox securing bolts.
Fit outrigger bracket without bolts. Put box in neutral. Rotate final drive sprocket by hand and feel how much force is required to rotate it. Fit and tighten outrigger bracket securing bolts. Recheck freedom of rotation of final drive sprocket, it should be same as previous test. If not you might have to shim the assembly, but that is another story!. Remove front outrigger bracket front nut and washer, leave rear one secured. Cut and file a small piece of aluminium that you can just push into the space between the front securing bolt and the end of the adjustment slot. Find a large washer that will cover the space and keep this packer from dropping out. Fit the nut and tighten. This packer will stop the gearbox from being pulled back by the higher loads generated by the rear chain. This is a usual fault and causes much friction between the high gear bearing surface and large bronze bush. If you can prevent the gearbox being dragged backwards, you prevent power being lost by the friction that eventually wears the bronze high gear bush. Personally I have found that if you use castor R 40 in the gearbox you will have a nice silky smooth change and the wear in the box will be greatly reduced.