I just trimmed a set of BMW bearings last night. I believe it's better to trim equally off both sides, otherwise the tang would be on the edge of the bearing. The bearing I use are .950 (approx) wide and they need to be to .860" wide to fit into the type 1 saddle with no overhang. This leaves about .090" from the edge of the bearing to the tang. If it were all trimmed off one side, one tang would be very close to the edge. The oil hole has to opened anyway, and it seems it's not in the same place in all cases, so it has to be opened for the case it is being used for.
Udo, are the thrust pieces you have pictured there cut from the BMW bearing or are they part of a type 1 or 4 bearing? I measured the thrust flange thickness of a BMW bearing and it's really close to being perfect for the standard width of the thrust saddle of the case. (.095" thick)