rbterhune,
In my personal experience, I had never worry about how flat the sole it is, all of my planes came either from eBay or flea markets, I’ll do the whole restoration process and just try to “flattened” the sole on a piece of granite with some 220 wet/dry sand paper, I won’t stress out on this, just a quick run on the sand paper, I see very hard that .003” will affect on anything at all, after all we are working with wood and not making highly precision machinery.
If you need something to be dead flat, perhaps you need to look on the premium planes.
I know a guy (from another website) who grinds them off and claim to hold a tolerance within .0005” of flatness on a No8, I haven’t use his services yet so I can’t verify if this is true, but again I don’t worry about that, perhaps a crack will be a red flag to me.
-- The things I make may be for others, but how I make them is for me.
