I eventually bought a battery - at a local bike shop ,which specializes in selling pirate parts to (what seems to be) almost all bikes on this planet.
According to their catalog, the "correct" battery for R65 models from "1984 - 1995" should be a 30AH battery (C60 -N30LA) -the same battery (according to the part list) which should be used for R80 models.
The guy at the counter probaly noticed the disbelief in my eyes - so he showed me the catalog........
the "correct" battery (according to the list) for R65 models - 1978 - 1984 is a "MS 12 - 19"
After some initial doubts, I decided to buy the (wet sell unfortunately) 30 AH battery - at the rediculous price of ZAR1048.00 . Hopefully it will keep a smile on my face until end June this year - it only carries a 6 month warranty........
Regards
Danie