Hello, Xausa:
I have sent you a PM regarding your system to make 8x60 from 9,3x74R, but other people may be interested, it is really plentiful in Spain. Do you use special dies or just "cut and form" with the standard sizing die in a single pass? A friend of mine makes 8x75RS brass from 9,3x74R for his double, but it is the same case length necked down.
I heard from another 8x60 owner that directly shoots 8x57 cartridges in his rifle (I suppose the bullet diameter is the same or lesser...). The resulting case must be, er, weird. He has survived to this day, I understand...