Can any one inform me of the correct size for the nuts that retain the inner gearbox cover on a 74 commando? Somewhere between a 1/2 & 9/16 as far as I can tell. Would also seem to be a tight squeeze for any Socket to fit over some of the nuts as well ( not much clearance between nut and cover). Is there any special socket I may Need? Any help would be much appecciated.

Only the engine and gearbox of the commando have any BS/whitworth nuts/bolts. The ones you mention are one of them. IIRC It is bigger than 1/2 at .525" It is probably 1/4whit(3/16BSF). You also need a fairly thin wall socket. I use my snap-on 6 point 1/4' drive, since the 3/8 drive socket is a bit fat. most other commando chassis hardware is unified (american-mostly fine thread)

Thanks Mate. Much Appreciated