This is what Silvio sent me with regards to head specification.

"39mm inlet valve, stock is 36mm
33mm exhaust valve, same as stock but sodium fitted for high temps
enlarged valve seats
shortened valve guides for better flow in bronze for less friction at high temps, stock only exhaust is in bronze
polished and ported ducts
cnc machined valve seats, vacuum checked for optimum seal when valve is closed
uprated valve springs
skimmed and combustion chamber recess
special tcrime cum inside"

An additional note is:

"Head prices will increase soon, valves will increase soon, lot of labour, is hard to find good heads.......and need days and days of labour !"