ronal is a german company, so hard to believe that yamaha used them as oem, could be a dedicated kit...
in this month's motociclsimo d'epoca issue there's a good article on all the aftermarket cast wheel industry that started in italy in the 70's: campagnolo, EPM, OZ, etc.
they were making a point of how unregulated that whole industry was with little in tems off quality assurance and product testing.
if they are magnesium indeed, wouldnt even consider using them unless you put them through a professioanal x-ray check