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I'm looking at couple of 12G940 Cooper S 11 stud cylinder heads for a MK3 S, they're stamped near the thermostat housing with 12G1805 and below this it's stamped with a K and the other one is stamped with S, I just wondered what the K & S marks meant?

Ant thoughts would be appreciated thanks in advance.

I reckon I can still muster an Ant thought or two. Don't expect any more though

The K's & S's you refer to are inspector approval stamps. There are other letters to be seen round there too sometimes.

Perhaps it is just a mark to quckly tell that it is a large inlet valved 12G940 head rather than a small inlet valved one as fitted to the Mini Clubman 1275GT at the same time, where K is for Cooper or S for Cooper S. Think there was three versions of 12G940 head available from the factory for Mini's around this time of the mk3 Cooper S, 1969-71 and just after,
large inlet vave, 11 stud - mk3 Cooper S.
small inlet valve, 9 stud - standard mk3 Mini Clubman 1275GT.
large inlet vave, 9 stud - supplied in the BL factory optional extra 'S' pack available for mk3 Mini Clubman 1275GT when the mk3 Cooper S was discontinued, to give the 1275GT about the same power as the Cooper S. Done as a marketing thing from complaints at the time from the discontinuing of the Cooper S. Info on the 1275GT 'S' pack here,
http://mk1-performance-conversions.co.u ... /gts_2.jpg
http://mk1-performance-conversions.co.u ... _press.jpg
http://mk1-performance-conversions.co.u ... _s_kit.jpg

Cheers, thanks for the info nice to know.