The 1020 is the early cross flow, baffle-piston blackhead:

http://www.webra-austria.at/motor.ph...ype=AERO〈=EN

the 1024 is the side exhaust Speed:

http://www.webra-austria.at/motor.ph...ype=AERO〈=EN

and the 1030 is the rear exhaust Racing:

http://www.webra-austria.at/motor.ph...ype=AERO〈=EN

there is also a 1033 long stroke rear exhaust:

http://www.webra-austria.at/motor.ph...ype=AERO〈=EN

I have the first three (pictured in reverse order).

David