To the best of my knowledge
300 - This was the first design, Shoulder wing 300hp.
300 Special - very small number built, single seat version of 300
300s - Single seat version - low wing, with the wings clipped and roll rate increased. For improved visibility and results in cleaner Snap entry and exit.
300L - Single seat version of 300s
330 S & L - 330hp - version, larger elevators and I think increased rudder area. very few of these exist one is owned by Peter bessenyie.
I have flown in the 300 - and what can I say - PHOAAR Fantastic!
If you want a try yourself in the UK, flights are available from Power Aerobatics . see
www.power-aerobatics.co.uk for further information.
Best Regards
Biggles