Thanks for all your advise Roelof, much appreciated.
Will try the buggy engine for sure.
On the other hand, I have two worn out 35+21 based engines. They got the 7x19x5mm bearings with metal shields. Would you run them in the rain, or is it senseless to try without rubber shields?

On more question: How do you "set-up" a rain engine? My strategy so far: head gap like normal (0.7mm), very hot plug (5 or 6), lexan under the motor mounts and aluminium foil around the cooling-fins. I know a shorter cooling head would keep the temps up nicely, but sometimes the track dries during a final and then you are glad when you just can remove the foil and adjust the carb for better performance.

Thanks again, Stefan