stijn,
A lot depends on what you are looking for. For example, for a 2.5cc stunt you might consider the LA or a TT. For racing you might consider the MVVS 2.5 which comes in either diesel or glow (as did the G20-.15 (2.5cc). For diesel, you might also consider the PAW.
If you are intent on getting your Dad's engine in a plane, as Jim said, get someone to make you a tongue muffler (I forgot about the muffler ears on the crankcase). Before you invest a lot of money to get it set up you might want to bench run it and see if everything is OK. It may be hard to get parts, except perhaps bearings.
Good luck with it.

George