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Have you decided what to start on? (stanley)
Could always mill off ghe posts in one go, close to the base, and make four bearing blocks that bolt on.
As for doing it in the mill, can you use a drill size for which you have a collet? Then ream behind the drilled holes. Just my 2 cents.
And two cylinders right? Zee the lathe is fine as long as you can get the height right. Fortunately the cylinder bores and crankshaft hole(s) should be at the same height.