The Mk3 rear wheel is considerably more complicated to lace than other Commando models.
Before you try re-spoking the rear wheel of your Mk3, be aware that there are 3 (as in THREE) different spoke types used on that wheel. The long spokes mount to the disk-side (RHS) hub, but the opposite hub uses two different short spokes, depending on whether the spokes arrive from the inner or outer side of the hub. These two spoke types differ in their head angle, which is pretty subtile to determine. Do NOT bend the spoke if it does not easily enter the rim; this condition occurs when you have the wrong spoke type inserted. If you order a spoke set from, say, Walridge, they will ship them bound into three bundles; it will be up to you to distinguish the two types of short spokes and where they go. Once you get past this small complication, the process is straightforwat, as long as you have measured the original wheel dish (the "offset") before you have disassembled the wheel, and can restore it. The longer spokes are laced in a 3-cross pattern, the shorter spokes in a 2-cross pattern.
If you have the time and aren't put off by what I've said, then, as a hobbyist, I recommend that you give it a try. The process is a thoughtful one, and is fun, but be prepared to spend most of an afternoon, and a few beers, on that rear wheel. Otherwise, pack it up and send it to Buchanan's or Walridge, who know Norton wheels very well.
Tuning the wheel involves both concentricity and transverse (wobble) adjustments. Remember that when you are making a transverse adjustment, you must tighten the spokes attached to the hub that is in the direction of the correction, AND at the same time loosen the spokes attached to the opposite hub; this approximately preserves concentricity. Conversely, when making a concentricity adjustment, tighten or loosen an even number of consecutive spokes together, as this approximately preserves the transverse adjustment.