Hello Mikko,
I don't have any experiences with these heads either, but I thought that the only one that does as far as I know (in my country) is Henk Hendriks (
www.hotrod.nl, no info on that engine there tho). He owns one of the oldest VW aircooled shops, is very knowlegable and uses those heads in his Nitro'd tube framed dragster in a 2866 cc type 4.
My gut feeling is that they are totally unsuitable for more than 402m street driving, for the reasons you already mentioned.
As you will have guessed, Henk only drag races with that car.
Best of luck,
Walter