Jim Robertson
What SB or ASB or any other safety bullitens has Subaru released regarding that engine? Just because you found an engine (out of a car) that doesn't have any bulletins against it does not place you in a better postion in regards to running a Rotax. The company that used to sell those Subaru engines for aircraft is no longer around, so support and parts may be hard to come across.
The Subaru engine also had a poor power to weight ratio. With that said, the choice is yours! Briggs and Stratton (lawn mower), Subaru (Car engine and conversion company no longer around) OR Rotax (full support and parts available)