Debbie,
I would not use threadlocker of any kind on cylinder head, or barrel fasteners. How are you going to be able to re-torque?
On the engine, I use loctite on any fasteners that are not able to be re tensioned, without a strip down. I.E. conrod bolts, flywheel bolts ETC.
Then on the frame I will use loctite on my rebuild on any bolts/nuts which do not have a thread lock mechanism, say spring washer or nyloc nut.
There are a lot of nuts on the Commando without locking, so my quess is the commando does not transmit much vibration to the frame area? But again a dab of loctite not only holds the nut tight, but lubricates on assembly.
Phew, hope this makes sense, just my two bobs worth!
Richard