LAYDOWN (AND OTHER) GEARBOX QUERY

There is a bronze thrust washer between the sleeve gear and the mainshaft 3rd gear. You will need to make it thinner. Try finding one which is worn thinner than the one you are using - failing that, machine yours down a bit. Be careful - you can't put the metal back later.

Another way to gain end float is possible if you have a pen steel washer between the main bearing and the gearbox shell. It's there to stop oil flowing out of the box via the main bearing. This steel washer is unnecessary if the bearing is shielded. No need to have two shields. If it is shielded, you can delete this washer, and gain some needed end float. If your main bearing is a bit worn, replace it with a shielded one. Rubber shield bearings are usually shielded both sides, and labled '2RS'. Remove one of them before fitting, leave the one facing the outside.

This applies to any Norton gearbox (pre-WW2 doll's head, vertical, and horizontal), but not the AMC box

Isn't this something to worry about only with roller (not ball) bearings? The alloy case expands more than the steel bearings inside it, so if it all spins freely when cold, surely it doesn't need any extra float? Unless of course yours is all jammed up when cold?