Assembling a cylinder head takes some work and patience.
Done with the guide replacements I got my seats adjusted by Cala in the impressive Sunnen VGS20 and they now check out within .00015" (Inch) when we take the concentricity readings.
It is a big difference to use the mm indicator which reads in .002 mm increments rather than the common .001 Inch, sure it`s the same factual but the gauge action is so much more obvious.
Most of the assembly is like other heads but, getting the valve spring cups, or "tin`s adjusted and the rocker arms shimmed to the right position takes some time and repeated mock ups where one has to tighten everything in the right sequence, rocker arms, rocker box and check free movement, take it a part, adjust do it again, take end play, shim and over again. (you figured right, it´s a lonesome deal and requires a solid rock channel...)
Anyway I use cast Alu. "tin´s" FHP style, and I had to replace the front Intake one, so I prepared a new one never used, and that took some work, as I had to open the spring cup dia. and mill the rocker arm path for clearance, weld and relocate one threaded hole for the cover as well as weld the cover to facilitate machining clearance for the roller .
The old FHP spring cups does not locate like the stock ones with the guide thru the tin but still need some help getting located so I machine the Valve spring bottom cap with a short flange to snap around the guide flange and fit to the hole in the cup. After two nights I´m ready to shim spring height and close up the front head and that´s usually only one night´s work, I´m happy.
Update: Back to using original tins, the Al has a tendency to crack due to spring loads and action. also the tins provides better room as they are for the springs.