Joel,
This will really change the subject, but you brought it up, so they can't blame me. Actually the question crossed ny mind as I was reading Ron Kwas' comments in the 120 Index.
Yes, I would think that, all other factors being equal, the longer legs would give you better mileage, at least, in theory. I tend to think, however, that driving habits generally have a bigger impact. Witness how people win those economy runs; sure, tuning is a factor, but how they drive really makes the difference.
My 142E came to me as an automatic and I swapped in an M41. I'm assuming the differential is a 4.3 (correct me, if that's wrong) - no tag, so I can't be sure. I have no idea what the OD has done to the final ratio, particularly since I don't know what series it originally came out of, and at he moment I'm running snow treads I borrowed from the 245. Oh yes, and I rebuilt the speedometer with pieces from two other ones. So I really have no idea to what extent the red ribbon reflects my actual speed. The seat of my pants tells me the speedo as about 5 miles pessimistic. I can resolve all these doubts by timing myself on a measured mile, but I may have to go up to Aroostook County to find a piece of I-95 where traffic is thin enough to do that accurately -- maybe Montana.
Bob S.