Ehsan,
The Mystic 90 is a bit of a puzzle but you are right, 90 2-strokes were not being used in those days - at least not for competition in F3A. The issue is that during the 90's, the four strokes began to be more popular and although we know that Hanno didn't use a 90 2-stroke or a 90 4-stroke in competiton, this model appears in his hands in a few photos I've seen. My feeling is that that model was really a Mystic 60 but it was designated as a Mystic 90 by the manufacturer, EZ, to encourage the sale of equivalent 4-strokes. Even the Mystic 30 was released with some reference to it being a "50 size" model suggesting the use of a 48-53 size 4-stroke. In fact, even the earlier Supra Fly 25 and Supra Star 25 models were advertised in this fashion.
The main thing I would like to clear up is the number of scales that the Mystic existed as. We know it existed as a 60 size model as well as a 120 size model but what's not clear to me is what the Mystic 90 is. Either a Mystic 60 advertised for 4-stroke power or a slightly larger model than the Mystic that Hanno flew with the OS 61 RF HS in Austria. I suspect, the 90 is just a marketing thing and it is actually the same size as the Mystic 60 that Hanno flew.
I believe I actually have some further info on this from a fellow modeller in England who has (had) an EZ Mystic 90 ARF kit. What I can't remember is the scale of the model. I'll have to see if I can dig that info up as, in retrospect, it is golden info! He kindly took the time to measure things out for me so I might, after all, be able to re-create some semblance of Hanno's Austrian WC model.
Regarding the Supra Star, I'll get back to your email as soon as I can.
David