I was going to order from ebay but with the grass growing so fast I figured I better get on it. I paid $62 each and even though it was more expensive than ebay, I was glad to support the local small engine guy who had them in stock!
As far as setting the air gap, I used a feeler gauge...kind of.
I wanted something that would fit under the whole coil so when it sat against the magnet I could simply tighten the screws.
Using a mic, I found a piece of glossy junk mail that was close, then added a piece of blue painters tape to get it to just over .013".
Attached the coil spaced away from the magnet, inserted my 'gauge' and loosened the screws. It clicked against the magnet, I tighten the screws and turned the flywheel to remove the 'gauge' and then checked with a real feeler gauge.
It was right around .012.
I did notice for some reason?? the air gap on the second coils got smaller as I tightened the screw so I had to increase the thickness of my gauge slightly to compensate.
How ever you do it, I would definitely check it with a feeler gauge.