RE: Numbers for ST G21/35 DDD head
Yes, very fortunate.
The silencer adaptor sold by MECOA for the ST equivalent engine fits perfectly. So, when I ran it I fitted up the adaptor and a spare KAVAN 'strap-on" silencer. Worked a treat.
Despite its 'Soviet' industrial grade finish my KOMETA is suprisingly well made (apart for the contra issue). No fuel leakage it the front ball race despite the race being 'open'. There is no shield on the prop driver. The gap between the race and the back of the prop driver is substantial. I suspect race life will be short due to dirt ingestion. I may exchange it for a sealed race when sorting the contra. I expect the race is a standard metric size.