RE: First Gasser. Which engine. What do else is needed?
The Homelite 45cc engine is an awesome engine! I convert them along with the 33cc and 38cc sizes as well, but the 45's are the best for stunt planes. I am currently having some carburator manifolds machined to convert the new type of Homelite 45cc engine. All of the refurbished old type Homelite 45cc Timbermans are no longer available through Harbor Frieght. Every now and them you can find one on ebay but you have to know what your looking for.
The new type does not have a bolt-on manifold which makes it difficult to convert if you don't have a machine shop. My new manifold forces me to install a remote crankcase pressure tap on the engine block and carburator to allow the carburator diaphram pump to work. This is not a big deal to do, you just have to know what your doing.
I normally sell a brand new, beautifully converted Homelite 45cc engine for $250.00. That includes a polished muffler and prop adapter, engine mount and rails and modified carburator with a straight-shot linkage. The engine pictured has the old bolt on manifold. This type of manifold you have to use a bel crank to actuate the throttle. Tricky, but do-able.