Shes a beauty Paddy - I always did like the White framed SS - nice crash mushrooms as well.
Nope - checking the sparks like that has a high chance of blowing bits
I must search for Haynes as I aint seen it for a while - as I remember you make a wooden block (honest) to accept and insulate a spark plug, then have a moving nail/pin so you can push it up to the outer electrode and then crocodile clip it or bolt it to the frame somewhere to ensure a good circuit.
Throwning some new plugs at it might be an idea.
Can you smell petrol at the exhaust that isnt firing?
Is the petrol tank vent clear / can you hear fuel returning to the tank when the ignition is on (fuel pump running).
The HT leads screw into the outlets of the coils (under the tank) I guess it spossible it could of come undone or the lead is faulty.
My always takes a good while to start after a lay up and I usually end up 'jumping' her off my car rather than burn a battery up - even then she can run on one cylinder for 30 secs or so for some strange reason know only to herself - but always comes good.
Good Luck - Frank