how the hell did you know that LozMan ?
Rotax's are my thing Hoony, currently I would have 6 x 125cc engines (2 type 124 and Can Am MX 6) 2x Type 128 engines 1x type 129 and 2 x type 256 250cc twin engines here. The Aprilia GP engines were all derived from these motors.
Type 124 (MX6 engine with alternate clutch cover and cylinder reversed later used water cooled cylinder)
Water cooled cylinder kit for Type 244 (250cc)
Type 128
Type 129
Type 256
All use 2 type splines 18 or 20T