Ok, there is a happy end to this story :-) I found original snorkel amongst other bits i have been given with the bike, so simply cut the original one. Fit between K&N and original snorkel was still a bit loose, so i have stick some thin rubber pads under the filter lifting it slightly, and now there is a nice, tight fit.

Inlet diameter is slightly reduced now, as cut snorkel s slightly smaller than this toilet rubber, but i think is the same diameter as stage 2 DNA cover?