Thought I'd throw this one out there after seeing this

Purists stop reading here.
I'm toying with repowering one of my Maicos, but I'm not keen to do it unless i can find an engine that looks 100% like it belongs there.
There is a pretty specific set of criteria and i haven't found anything yet that fits them all.
the criteria are:
- Must fit completely within the stock bodywork, although there is a lot of space.
- Must be electric start, otherwise I'd have to cut the body.
- no external visual difference, except 2nd exhaust pipe.
- 300cc to 500cc side by side twin.
- preferably motor is produced in Germany or Austria.
- Must be chain drive. Chain preferably on the right side of the motor.
- Must be a manual.
The ROTAX pictured above looks ideal, but I suspect its not electric start.
The Jawa 350cc twin would be sweet if it had electric start.
BMWs are out with the boxer thing.
Any ideas?