I have an extra Estes Saturn V Skylab (main body tube is a bit squished), but the Skylab vs Apollo doesn't much matter here. What I want to do, because I can (try), is modify it to be a cluster of 5 (probably 18mm), gap cluster them to a second stage with another 5 (also probably 18mm), and stage that to 1 motor in the 3rd stage. More @Wikipedia
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