Looking over all the pics they provided for the 10cc engine, it seems any of the 1/4-32 thread plugs should work. There are a lot of web sites offering them.
I am planning on putting this engine in my Stinger 60 which has been sitting in the original box for the last 3 years. Finally a small ignition engine made to actually fit in a 60 size plane!
The Stinger lends itself to many engine possibilities. Also a good choice for a sport plane with everything out where you can get to it is the GP Big Stick 60. I have one of those also and had originally planned on a 16cc Echo conversion for it but the weight was a bit much for the nose. I may have to just buy a second Evolution 10cc now.

The ignition is smaller and is probably very efficient power wise, so you could probably run a 2 cell Lipo at 7.2 volts and 900 mah and have plenty of battery left after 5 or 6 10 minute flights. Both planes I mentioned have room to spare in the tank compartment for the ignition and Lipo battery. Just looking at the plans and getting some ideas. More cheap flying fun!!

John