Great pictures and nice bikes. 6'3" with 33" inseam. If that is cycling inseam and not pant inseam, you are more torso than legs. So I see how you would be challenged standing over the 62cm Merckx. Bet you enjoyed the nice long top tube though with your torso length. By contrast, I am 6'1" with 35 inch cycling inseam. I would really like that 62 and seek bikes with that tall a top tube...though modern bikes now tend to have sloping top tubes with easier standover while retaining tall head tubes. I also don't like to ride with the bars in close so a big frame like that Merckx always works for me.
There is a beautiful 62cm on Craigslist I am trying hard not to buy right now where I live. Indeed your two Merckx bikes are dramatically different in fit. Me? I would prefer the taller bike even though I am shorter than you. Goes to show how proportions and preference trump height when it comes to bike fit.
Thanks for sharing your story.