If you want to take the sump plug out a 1 1/2" socket will work unless you have the early frame and then you are going to need a special thin ring spanner to get under the frame support, they are available. The 1 1/2" socket also works fine on the drive sprocket left hand nut if the inner mainshaft is removed. Don't ask how I know. The mainshaft inner cover nut can also be removed with a 15/16" standard socket, especially if you use 6 point sockets. Usually you can get a 7/16 (real tight) over a 3/16 BSW bolt, like the transmission quadrant bolts and some of the engine crankcase nuts. You will need at least one 1/4WW combination for the head and the crank nuts/bolts, 2 would be a real plus. A 1/4WW socket will be necessary and it will probably have to be ground down thinner (like mine) to get the nuts off the con-rods and as previously stated for that central nut on the barrel, you will have to grind down a 1/4WW ring spanner to get into the close fit central nut by the barrel.
Hate to say it, but in a previous life I have used 14mm for the 1/4WW, but I wouldn't recommend it, especially not a 12 point.
It is always nice and better to have the correct tools, just watch Mick's DVD's and you will know what I mean.