I would braid some copper household stranded wiring (like old extension cord) into a ring as a secondary ring if you are in a bursting hurry to get the SIM on your bike.
Piece of copper pipe is not a goodly idea.
ALWAYS tight the big nut goodly and then recheck it is goodly tight with the engine fully heat soaked the first couple of runs. If the nut walks loose and rattles around it can erode the threads in the cylinder.
You will want to upjet, which is hard to find jets for Gurtners... or switch over to a SHA.