Feed rates, pulley sizes? - sqaure dial machines

As a result of my belt length woes I am puzzled as to feed rates. Terrie tells me that there is only one Monarch flat belt at 37 inches long, way too short for my machine.

There are two different spindle drive setups, one with the flat belt running on the spindle, the second the flat belt running on the convex aluminum sleeve.

There are (at least) two different gearbox driven pulley part numbers: EE1009 and EE19889.

To have the same feed rates, the type running on the spindle would have to use a smaller driven pulley than the aluminum sleeve type, which would require different belt lengths. However, to use the same length belt, the spindle driving type would have to use a bigger driven pulley and conversely the aluminum sleeve type would have to use a smaller driven pulley, which would then produce different feed rates.

Making it more puzzling, I have three data points: mine, a friend's and Labeeman, whose lathes use belts 38-38.5 inches long, which goes counter to what Terrie is telling me.

Mine and my friend's driven pulley is 7&3/8 inches OD.

I believe my 1951 manufacturing model with only 6 cutting speeds has a larger pulley on the feed drive then thread cutting models. Also, later on they added a thin aluminum pulley to the spindle itself, seems possible there could be a parts switch.

Aluminum on spindle approx 2.4"
Drive pulley approx 6 15/16"
Can't read the writing on the Gates belt, sorry.

You are way over thinking this problem. The feed rates are approximate, 10% more or less is meaningless. I use a serpentine belt for last 12 years, mine is 1960 with the crowned sleeve on the spindle using a NAPA belt 25-080384 running grooves down.

I am using a 38 inch serpentine belt as well. It was Terrie telling me that there is only 1 flat belt for all 10EE that I am trying to figure out. I certainly wouldn't say that she is incorrect, it just seems that one belt length cannot cover all the different mechanical arrangements.