Clearly the dimensions of the frames given on the Colnago site simply illustrate the way in which Merckx designed each frame for a specific purpose or even a specific race. Presumably he would have a shorter top-tube for stages in the mountains where he might expect to be on the tops, or the hoods, and a longer one for flatter stages where he expected to be on the drops for longer periods and more stretched out on the bike.
VAR's "Le Petit Livre Jaune" gives an example of Merckx's frame as having a 590mm seat-tube, a 570 top-tube, with chain-stay length of 425mm, and a front end clearance of 600mm. Fork rake is 40mm and trail 60mm, bracket height being 270... All measurements are centre=to=centre. Set-back of the seat tube is 165mm
VAR also gives dimensions for Zootemelk's frame and these differ noticeably from those given by Colnago, they are; S/T 545, T/T 545, rear stays 415, front clearance 595. rake 40mm, trail 60mm bracket height 270mm and set-back 150mm.
Sometime ago I read a statement by Merckx in which he said that most of his frames were identical and that for any given race he would just change the length of his stem or raise the bars, and slide his saddle backwards or forwards in its cradle. He further commented that he thought his frames to be very "standard for a man of his height and build."
I have another couple of articles about his frames somewhere, and will post the figures if I can find the magazines.
Norris Lockley, Settle UK