I think the range of 54.5 to 58.5 is created by unfortunate ommisions and mistakes in the Colnago drawings that appear in the Negri book.
If you look at the first drawing (Sig. EDDY) it shows a measurement along the top tube of 54.5 BUT above that in a small box is the center to center measurement of 57.5.
The next Merckx frame, for the 1970 TdF, is shown as 58 c-t-c in the small box (no measurement above top tube).
If you jump to the Merckx TdF bike of 1972 the drawing has again 54.5 but the upper box, which should have the top tube measurement, is blank.
The 1971 Merckx bike has 56.5 along the top tube with the word "interno" (internal).
The 1973 Merckx San Remo bike has 54.5 in the upper box. I have a feeling that's a mistake...that the number along the top tube has now been transposed to the upper box where the c-t-c should be.
Maybe you all you Negri book owners can take a look and chime in about what you think.
Angel Garcia Verona VR Veneto Italy, way too late to be thinking about this
I think Ed Granger hit the nail on the head. I happened to have the Negri book handy this morning, so I checked the drawings/specs for Eddy's frames. The book has seven different drawings for Eddy (and a bunch more for other pros of the time). Of these seven, only four include specs for the stem length. Of these four, threee are 12.5, and the last one is the 12.2 stem for the hour record bike.
It would appear that Eddy generally rode standard length stems, and that the 12.2 stem was a custom size, fabricated by Pino Morroni (in Detroit if I'm not mistaken?!).
BTW, the drawings for Eddy's frames show that the top tube lengths he ordered, varied from 54.5 to 58.5!!! In between, he also ordered frames with 56.5, 57.5 and 58 top tubes. Molto interessante...
Miami Florida USA