Specs for Valve Grinding Stone for 38 Tplane

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I have located a valve seat grinder to use on my '38 Terraplane 6. My question now is what size stone and mandrel do I need to clean up the seats? I know the angle is 45 degrees, but after that I am lost . Can anyone tell me the dimensions of the stone and pilot that fits into the valve guide so it won't "wobble" while it spins?



Thanks for your help, again.

Paul Caldwell