Head work on my Sprint

[73sprint]

What if the the valve retainers are ground down by a few thou ?. I now have clearences of 17/18 thou on the inlets but it seems marginal to me because some shims are slighlty lower than the retainers. I have turned the cam repeatedly by hand and checked each valve and it seems good. If the retainers could loose some metal i cant see a problem but is anyone going to correct me ? The engine shop have tipped the valves and say this is what they have done to some stags locally.