I have seen him answer this question several times..."Plans, piss on that, I'll show my plans" He then taps on his head and "that's where my plans are"
Although I am sure his answer is partly an act, he is really old school and thinks 3-D in his head. I have never seen him work off a drawing. Mostly it is his memory of how the old ones were put together plus his imagination.
He has at least 6 distinct "models" I have seen and rarely are the same models identical.