If it gets stuck like that, you should be able to just take the velocity stack off right there in the field and use your fingers to pop the plunger loose. Bring a small flathead screwdriver or a socket wrench with an 8mm socket with you for loosening the clamp on the stack.
Glad to hear it all works like you wanted it to. A stock spark plug (NGK part #CR7HSA) should be available locally for $3-5. They're pretty common.
When you're ready for the CDI, just let us know!
