With the JB weld set I've re-bored the seats for the valves and everything now fits snugly. The ally braze seems to have worked very well, certainly an option for fabrication.
I drilled the stud holes for fitting the valve assemblies by clamping the cylinder head seat face to an angle plate and lining up the inlet/exhaust port face with a set square, which is at 90 degrees to the valve faces.
Then drilled through, using the valve assemblies as jigs, and tapped on the pillar tool
8BA studs for the exhaust valve
Both valve assemblies in position
Here's a couple of pictures of the combustion space. I cleaned up the inside in the same way as I did the first time, together with a bit of tidying up with a burr in a Dremel to smooth the transitions a bit
I still need to drill through for the spark plug but as I've not decided which plug to use yet I'm leaving that for now.
I guess it will do but there's a nice new cylinder head casting on the bench whispering "do it properly" to me. I shall turn a deaf ear for the present as the inserts have become something of an experiment and I'll carry on with the botch.