Probably too much info but here goes...
The 13$ Emgo Tail light cited in my previous post has the same center to center mounting as the original MZ item.
Need to remove the too short (5mm) mounting studs supplied and add spacers and longer bolts and nuts.
Otherwise the light socket backside interferes with the oil tank.Aluminum spacers I used happen to be 10mm thick and about 3/4 inch outside diameter.
Bigger diameter is good, if you have any doubts, reach back and touch the tail light sometime at speed
and you'll see how it really gets buzzed.The original MZ mounting bolts are 6mm, so some plastic tubing on the bolt where it goes thru the original rubber washers and backer takes up the wiggle.
I bolted it from the oil tank side and added lock nuts where it threads thru the light .
Note this light grounds thru the frame, so a jumper is needed to connect to the MZ grounding spade connector.
Good luck.