lister cs 6/1 valve recess

I am in the process of restoring a listeroid sc 6/1 (INDUNA) .The valves are in a very bad state and needs to be replaced. The valve recess is 4.5 mm when close and the specs tolerance is .050 to .100 (1.27 to 2.5 mm)looking at the valves it seats very deep . QUESTION :
Is it important to have the valve recess within spec. Should I skim the head to bring it to spec and than to shorten the push rods or set it correct with the tappet clearance I do not know if the tappets will adjust that much.
I would appreciate any experience suggestions

Those deep valve recesses will lower the compression ratio and impede the gas flow.
The reduced compression ratio may make it harder to start, and also affect combustion, i.e. produce white smoke. This may be tolerable to you, but if the engine is needed to start and work reliably at full power for long periods; then it ought to be corrected (because it's only going to get worse).
I'm not familiar with this engine, but would check with local engine re-conditioners if it is possible to have stellite valve seat inserts fitted.

Hi Chris,  I have much the same problem with a Lister 6/1 that I have. I guess the fix will need to fit new valve seats or find another cylinder head in better condition.
I see new Indian made cylinder heads appearing on eBay at £100. I guess it may cost as much or probably more to have new valve guides, valves and seats fitted to an old head but so far I have not looked into this.
I'll be interested to hear how you get on with this. Good luck.

Tanks for the response . Will keep you posted on the developments and and actions