The coils in Lucas mags are often the trouble. They contain thousands of windings thinner than a human hair. They can break and the mag will still work(sometimes), dampness can make this situation worse. If it won't start, take the cap off the mag, put a paper clip onto the mag body so that the end is about 1/8 th of an inch away from the little brass pip that connects to the spring in the cap. You should get a fat spark. If not have the coils rewound.
Turning the mag over without a grounding wire ( as above) or no plugs attached is a no no as it burns out the coil.
All contacts need to be clean in the cap and the point settings are crucial.
Valve clearances are also crucial.
Standard start for your set-up cold engine...Make sure you have a head of fuel by using lever on pump untill resistance is felt. 2 pumps on throttle, turn one blade to suck in. repeat 3 times to prime each cylinder.
Crack throttle just beyond fast tick-over.( they like a good gulp to start )NOTE MAKE SURE AIRCRAFT IS WELL CHOCKED,UP ELEVATOR LOCKED ETC. It will start suddenly without warning at a relatively high throttle setting.
Practice swinging using the centre of the prop blade, do not use the tip because 1) it won't start,2) you'll brake the prop.
Give it a really good swing,with practice you can get it to go over one and a half turns. Don't be scared of it..a half hearted swing will never start it!
Good Luck!