Given your wood working tools and experience I would get some wood and some plans and start building. That gives you infinitely more choices than kits (almost gone in that size) plus it's really fun and you can do it.

These days http://outerzone.co.uk/ is a great way to get plans, also AMA Model Aviation and Model Airplane News plans service. Flying Models is in transition right now but should be back in business soon. Your little HB 12 should be a good engine for all kinds of planes. Randy Randolph designed dozens of good looking, good flying, simply constructed models perfect for those engines. His plans are available at all the sources I mentioned. Semperfi, Chips (MAN), Nacho (FM), Dime (AMA), Miss Diamond (MAN) are a few that come to mind. Old Ken Willard designs are great too. There are many others too; browse and ask questions here.

I have an old OS Max 20 just like yours. The OS 702 muffler was designed to fit the 15, 20 and 25 of the time and it works great. The throttle arm on mine looks exactly like yours. It is a great engine. Engines like this are available on ebay pretty cheaply because not many people use them anymore, but they are excellent. They have the great advantage for a scratch builder that it is easy to build planes for them and have a blast with them.