"Ward, First of all, the shims were used, not new. The shims were
turned down on a lathe. How much do you have to take off? If its a
significant amount I would take it off the valve. They are through
hardened (consistanty hard throughout) and not case hardened (just
the very surface). Peter."
I'm not an expert, but it was my understanding you DO NOT want to take any
material off the valve stem, because it can lead to insufficient clearance
between the shim and the valve keepers, and can lead to catastrophic
results if the keepers release the valve.