HI Ian
I built and tested a Jodel D18 which had a VW 2 ltr engine in it. The aircraft is a good design (Properly built) so as far as the aircraft is concerned no problems. The engine needs to be tested on the ground for the usual things like oil temp, engine temp and vibration .
The EA81 supra has been used on this type of aircraft overseas all with good reports for what that’s worth. The Jodel if it is a D18 well left off at about 38kts and climb out at around 500>700 fpm at 60 knots. Hope it helps
Albert Cassar