I forgot to mention that I found a double row bearing that has the same inner and outer diameter but which is 14mm wide instead of 11mm. This would still allow the use of the cover ring. The bearing would be properly centered by 3mm on an undamaged portion of the shaft. The remaining 11 mm with 2 thousands play (each side) would be taken care of by the glue.

I looked at the set-up again and I believe the scoring happened because of too much initial clearance, which is still the case on the good part of the shaft. As a result the shaft turns freely inside the inner race of the pilot bearing without driving it. Using glue may solve that problem. I will also glue the outer race inside the krankshaft. As the surface in contact is greater there the assembly will loosen on the shaft side when I disassemble the trans again, instead of having a glued bearing getting stuck on the clutch disk.