Janet is right about finding more AMC info at the site she recommended. That is the official site for the AJSMOC, based in the UK. There is another, older group: www.freewebs.com/ajsmatchless/index.ht
based in the US. Some members belong to both, some to only one. The latter, which has no club affiliation supports The Archives, that I suggested to you in another thread, (timing). Your G3 is better known in the UK as few were exported to the US.
You have an AMC gearbox & clutch, fitted from 1957. 350cc bikes had a 3 plate clutch, 3 plain, 3 lined & the half plate. The clutch was redesigned in mid-1959 & clutch sprocket, (basket), back plate, plain & lined plates & spring studs were changed. The early items above and the later cannot be interchanged except as a set. Most other hub parts are the same.
500cc & 650cc engines had a 4 plate clutch until 1963 when the 650cc G12CSR got a 5 plate clutch. The 3, 4 & 5 plate clutches each had a different pressure plate with depth varying to compensated for the plate stack thickness.
The clutch nuts should be adjusted so that the top of the flange under the slot is even with the cup. Then tighten or slacken individually to true the pressure plate to the plate stack when it is lifted.
The clutch linkage in the gearbox is an over-center type using a lever & cam & proper adjustment is critical for ease of use. Slacken the cable first, run the central clutch rod adjusting screw until it bottoms, then back off 1/4 turn. Finally, adjust the clutch cable for 1/8in or so play at the control lever.
The most common cause of heavy clutch action on AMC bikes is the wrong levers. They do not have adjusters at the control & have 7/8in spacing from the pivot center to the cable center. Use of the much more common controls with 1-1/8in spacing causes a mechanical disadvantage & heavy action.
My G80CS bikes with the 4 plate clutch are so easy to operate that I can pull in the lever with one finger with effort & is quite easy with two.
If I haven't obfuscated enough yet, try again. Cheers, Don.