I tried to do something similar with ts150 but could not due to the head sealing arrangement, but did find that a Suzuki ts185 piston was very close to the mz ts piston which I think is different to the etz. the bantam big bore piston is a modified Suzuki ts185 piston. I believe the etz has a higher piston crown, but it may be possible to use the piston by shortening the barrel . by the way bantam racing pistons are available with a 15mm small end asper the mz in a various bores.
Bill