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Put your two blocks together, mount on a lathe face plate, then bore on a lathe. This will provide the best surface finish easily .
Put the same two blocks in the mill and do a a circular conical milled pocket. This provides the best alignment compared to separately machining the blocks.
Maybe do the same operation over a 190 deg arc on one block at a time.
These pocket operations would be done under G17 on a vertical mill.