laydown box and early 1950's clutch

The hand effort on my Dommie with 7/8" centres is much the same as 16H with 1 1/8" centres.  The 16H box has the same clutch.  So there's no point changing the levers.
Don't know about clutch springs.  I had mine out only yesterday - I thought they looked longer but very similar.
The main shaft has to come out to remove the thrust washer. So that means removing the clutch.  And not losing the 13 rollers inside the main gear wheel when the shaft is pulled out.  It can of course be done without taking the box out.
Do you have a laydown box manual? I have one here and can copy the pages if you want.

hello,
 
if the clutch was heavier. it makes you wonder if one of these would help make it lighter. i did buy one some time ago,but never got round to fitting it.

barry

https://www.feked.com/universal-easy-pull-clutch-lightener-system-3-settings-for-leverage-ratio-adjustment.html?srsltid=AfmBOoo_zgLzIpKfycd3wOiU9CspELd6HjwfO965R-0a9JEmT401hZTg

If a gadget like that will provide more force for less effort, it follows that the lever must move further also.  So you need to make sure you don't run out of lever travel.  It's exactly the same as extending the lever on the brake plate, or shortening the distance between handlebar lever pivot and cable stop.

.. with the laydown box and scroll clutch  actuation it needed a 1.1/16" lever to clear properly. A 7/8" one on the other hand made the front brake much better.

I think I'm right in thinking that the Domi has the misnamed AMC box with the lever and ball release in which case 7/8" may well be a good idea.

The laydown box does of course have the superior mushroom headed lifter which means all the clutch screws are tightened down fully as it lifts square. None of this messing about trying to get eve clutch lifting.

RGM list 2 clutch springs.  A lighter one for pre 1959 and a later heavier one.
NOC Dommie Service Notes describe the variations.

has a very high clutch lifter ratio. The 7/8" pivot lever was an attempt to moderate the excessively heavy clutch resulting. The solution is actually to alter the lifter profile on the clutch actuating arm.  I believe the Commando clutch lifter had a better ratio. Phil Hannam can give definitive information on that.
On a Norton box (whether 'upright' or 'laydown'), there is a quick-thread clutch lifter.  The ratio is fine.  The standard clutch lever on all such bikes has 1 1/16" pivot centres, and gives good lift. The lever weight is fine.  If you fit a 7/8" clutch lever, the clutch will be marginally lighter, but you have to adjust the clutch very carefully to avoid drag. 
Do not consider holding the clutch with the bike in gear when you stop, especially on a hot day. My bike has 7/8" clutch lever, and despite having a good clutch (with original Ferodo inserts in all plates), I do have to be careful to select neutral as I come to a stop.