Here goes, the head with issues now has new guides, cut & grinded valve seats, squared off bolt landings and a fresh coat of black cylinder paint. Ordered a guide reamer from Woodwards in US to ream the inlet guide which was too tight, and was a bit p.... off when I found that the reamer took out 1.5 thou more than it should... is that even possible, what's the point of an exact dimension on a reamer if it takes out more than specified...?
So the new inlet valve has a lateral play measured on the teller edge of 6 thou/0,15mm... I reckon it will work for quite a while anyway, the cylinder head I took off the bike had 8 thou/0,20mm play on the inlet valve, and the engine worked well with no blue haze or hick-ups.
Ariel W/NG '40 "Bitzer", Triumph Thruxton '04, IZH-49 '56, Tempo Standard 150 '54.