For this build, the difference between the old 700x28 and the new 650x42 is a reduction in diameter of at most 3mm. So, negligible in terms of standover height, but transformative in terms of ride quality!
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1987 Nishiki Prestige (now 650B!)
1981 Trek 710
198? Nishiki Olympic 12 mixte (now 650B!)
2020 Surly Troll fat-tire build