Gearbox Identification

The function of the spacer is to simply aid removal and fitment to the gearbox as unlike other models the mounting plates are fixed together with the welded cross tube that holds the swinging arm.

The early kickstart return spring is said to be more prone to breaking at the bend that locates it in the inner cover. That said the condition and quality of the spring and fact that most bikes see less usage than back in the day mean as with the spacer it may be a not a problem you face. Its not to difficult to change and apart from the need to hold the lever by bungee in return position to get you home its not a show stopper.

I assume the correct mainshaft to use the diaphragm spring type commando clutch is being used so other than that its no different to the later units. The parts are interchangeable apart from the above and the tooth form of some cogs but you should change cogs as a pair or the old will ruin the new anyway. So as with rest of the bike just check carefully what you have as things have obviously been changed from standard in the past.

The infamous layshaft bearing is the main concern and should be up graded without question. The thin area of casing between this bearing and sleeve gear bearing above it is prone to cracking (maybe what happened to the original case) which could be inpart due to the bearing its failing.

I would personally use the case if its good and spend money my on replacement of any parts within it not replacement of it for no reason. I don't care personally for the fact that numbers match it doesn't make a bike ride any better and as your original case is no longer there an replacement will also have different number it not something you can do anything about (well not honestly).

That's similar to mine which had an N prefix and Commie inner and outer covers. It also ran a Dommie clutch arm, one reason why the clutch wouldn't release fully! I still use the housing, supposedly a better aluminium than later ones, just a rumour! I'd check the clutch arm and if it's correct and no other issues there's no reason not to keep it.