you need a 650mm image circle for 16X20. The image circle for the 600/800/1200 is 310mm @ ƒ22 (for all the focal lengths), so you'd need to be focused fairly closely to even come close to covering. the FFD for the 600mm at infinity is 409mm from the film. with a little triangle math it looks like the lens would need to be 857mm from the film to throw a 650mm image circle. I'm not sure how to calculate how close that would be, but presumably it would be closer than 1:1.
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