For years a couple of engineer brothers from Toulouse developed an aero version of the Suzuki Bandit motor, built from the 1980s for 20 years or so – it used spay oil cooling.
They had some success with European microlights – with a built in reduction gearbox and manual clutch, it did not weigh much more than a Rotax, and had advantages of electronic injection, was quieter and smoother etc.
But no-one is going to make much of a profit with microlights and when they tried to develop a 150hp model for small Cessnas and the like they were swamped by paperwork and gave up.
Similarly lots of BMW boxer engines in microlights, at the 100 HP mark with dual ignition, fuel injection, et al, go well, sip fuel and are unbreakable, but difficult to go above 100 HP with them.
The South Africans linked with the Slinger (?) were developing a V6 related to the old Ford V6 Essex engines, 3 litres, very reliable and updateable, but last I heard they were also mired in the paper work bog.