2 litre VW
Have you considered the motor in the Grob 109b? It is a 2.5 litre 90 hp unit derived from a VW camper engine and with Porsche cylinders. You migh tthen enjoy the luxury of a 3 position prop too?!
Airborne Composites at Wing Farm Warminster will be able to put you on the track of one - they fix them up for the RAF as well as private.
Great engine provided you avoid shock cooling it.
All the best
HP