Mike, just a guess as to your situation, but if the base of the block is cupped yet the V-Block is true, then you could place a true cylinder (bar, pipe, dowel - anything on hand that is large enough in dia. to protrude beyond the "V") into the "V". Then place the V-Block with the cylinder against the fence of your table saw with a side adjacent to "V" down on the table, then skim cut the cupped side to establish the base parallel to the "V". Then sand the newly sawn base using the table saw. Just a thought.
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As I age my memory fades .... and that's a load off my mind!
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