Navigator Oil Grade.

No idea what the book says ,but if i was running one i would try Castrol XL 20.50 . Its probably what Norton would have specified if it had existed then.

Book specifies SAE50 engine oil in the gearbox.

... ATF in primary chaincases as it's designed to work with wet clutches. But I try to have just enough so that the bottom run of the primary chain just touches it. Difficult to tell with the unit tiwns.

If you type this into the search box of the home page, you should find a forum topic with the same title.

The last post in the thread, by Andy Sochanik, gives some expert advice on oils specified for Lightweights, and the best stuff to use these days. 

Peter

Navi (Jubilee & Electra too) gear box oil.

Book says SAE50, as someone suggested above.
You can also use EP80/90 - main secret is to keep the level topped as, as the shafts are one behind the other, rather than one above the other.

It means that the shafts can spin in fresh air if you do not pay attention, with disastrous results!

Later bikes (after engine 106838 & all Electra) have an obvious level screw.

On earlier bikes, the level screw is the cover screw to the left of the kickstart.

I've been using Smith and Allens high Zinc blend of 20W - 50 for the engine and primary drive. Also using their MTF90 blend for the gearbox.