If your's is a stock engine, it uses Rossi glow heads, the number 2 heat range is normal. There is no one making these anymore but the do pop up now and then on eBay, and guys like me have a few of them them squirrled away. Most people using these engines make or buy a head insert that take standard or better yet Nelson/Glo Bee plugs.
If you do not have the capabilities of machining one yourself, contact Doug Garabreth at
F1Cdoug@aol.com, and he can make one up for you as well as supply the Nelson plug.
You engine is a great unit being a copy of the Rossi MkII ABC. Properly broken in and fitted, it is good for 28K on 80/20. Some came with a tuned pipe and have higher timing than the open header versions. You can use a mini pipoe on the high-timed version with great success as well - all depends on you application.
These are high quality engines with good fit. Since they are so affordable compared to other high performance 2.5 racing engines, I like to suggest that people get a few and use them to teach themselves how to modify an engine for very high performance (these engines are capable of turning a F2A prop in the 36K range).
Good luck,
Ron Bennett