Engine Cutting Out! What to check?

I can see a couple of things with the plugs that may be an issue. Based on the coloration of the threads, it looks like they're a bit hot for that setup.

The timing marks look pretty good, but you could probably pull a couple of degrees out of it to get the timing signature to the middle of the ground strap. The goal is to have that discoloration about mid way through the ground strap with no detonation. Going to a cooler plug should cure any detonation you have.

Hope that helps some.