Mk1 cyl head removal

Get yourself a good Manual, Haynes is okay, and it will describe how to position the pushrods and how to lift the head to remove it. There's good examples of removal on YouTube. Some people hold up the pushrods using zip ties, other just their fingers.
You may find that by supporting the motor on a jack, removing the front ISO main bolt and head steady side plates you'll be able to lower the motor to give more clearance.

 It's a real pain the first time and a second pair of hands will help greatly.

...first time is a pain!  Try as I might the only way I could do it was by removing the front iso mount.  That allowed me to drop the front of the engine 1/2" which was the key to success.  I strongly recommend Norman White's Commando Restoration Manual - the bible as far as I am concerned.

I never had anything to advise how to do it the first time I had to remove my Mk3 head; just experimented until it worked.  You just need to lift and tilt the head back slightly without trapping the pushrods, then feed them up into the head with your fingers as far as they will go.  Try with one of longer inlets first and wiggle it around until get get it to go as far up into the head as it will go - this can to take one or two attempts to work out, but once all four are all the way up, with your fingers holding them in position the head can be tilted back more and will come out without having to disturb the front mounting.

You need to lift the head enough to disengage the pushrods from the rocker arms. Then move/turn the rocker arms so they're as far away from the valves as possible. This means you can then feed the pushrods up higher into the head to give you enough room to manoeuvre it off. Do the reverse to refit it. 

This is a correct way to do this but...Standing astride the bike, lift the head up and back as far it will go then with your hands either side of the head 'fiddle' the pushrods up inside (as above) with both hands using 1st and middle finger. Once all four pushrods are up inside, the head can be pulled back further, clear the bottom of the push rods and voila.
Might be useful to hold the head up early in this procedure with some wooden blocks or even the nuts that were under the exhaust ports.

As others have noted, Norman White's book is the most up-to-date authority, with many useful illustrations.

However, the official Workshop Manuals and Parts Books are still indispensable.

The Norton Commando group on Facebook has a large collection of useful material on its Files page, including PDFs of the above:

https://www.facebook.com/groups/10302209470/files/files

and use a second person. Also some people have taped pairs of pushrods together, especially when replacing head later. Just avoid dropping anything down the tunnels in the barrel!