I modify the Puch head for a second plug or compression release.
If you want the C/R for engine braking, you use the 10mm plug & a standard lever operated motorcycle release like this:
If you only want a release for starting, the 10mm hole takes a standard chainsaw compression release like this:
Stihl / Husquvarna decompression valve
Bigger chainsaws are usually equipped with that valve to ease the load on the pull start.