Hi Safetyman,
I'd suggest you buy yourself a copy of Newnes Motorcycle Repair & Upkeep Vol 2 from eBay. It was first printed in 1931 and reprinted a few years back. The seller has listed it under Motorcycle Manuals, Literature>Norton.
This was one of those weekly magazine things in 14 weekly parts that was sold through your newsagent and you bought a separate section each week. Vol 2 includes the weekly section that covered Albion gear boxes. It's the only decent illustrated workshop strip down and re assembly on Albion gearboxes I know of and covers all their range, 4 speed, 3 speed and 2 speed.
It should answer all your questions.
The early Albion boxes had just a plain pushrod which soon wore a hole in the outer clutch plate. They then changed over to the system you describe with the short mushroom like outer pushrod but I don't know when they introduced it. I know it is a common ploy to upgrade the earlier clutches with the later parts so who knows where yours fits in the equation. It may be original, it may not. Whatever the case, it is the better arrangement.
Cheers,
