I have one on my Huntmaster, after having the head skimmed I torqued it down on the bench then the next day torqued it down again, it went down quite a bit. I fitted the engine in the bike and torqued it down again, it went down more.
I ran the bike for a few miles and torqued it down again (the Huntmaster is easier for removing the rocker assembly) and it went down again. Did 500 miles and yes................ it tightened up again! After about another 1000 miles I had a slight oily-nes from the left cylinder so I bought a copper gasket ready to replace it, but being lazy decided to try to tighten it again, it went down again and cured the oily-nes
However 4000 miles later and it's still's fine with no leaks so fingers crossed, if and when I take the head off again I'll be using the solid copper gasket.
On my M21 I decided to use a composite gasket as the alli cylinder head had seen better days including welding a crack in the combustion area, like the Huntmaster it took a number of re-torquing sessions before it totally settled in (much easier with a side valve!) and it's been fine for the 2000 odd miles I've put on it.
Colin