Well, the good news is I have a copy of the 38 catalog...bad news, it is a poor photocopy and I really don't think it will scan with enough detail to see anything...that said, all of the illustrations of the 38 Supreme (men's and lady's) show the long chainguard while the deluxe 3rib tank bike has the vertical bracket chainguard-same with the 1937 catalog copies I have. I also have a photocopy of a march 1938 Cleveland Welding ad from The American Bicyclist again showing the long guard.
Fordsnake, the copies I have show the supported chainguard in 1937 unless there are subtle differences that I cannot see on the copies...
Also, the pics of the 40 Supreme have a different chainguard, not as long as the earlier styles and still non supported but changed to follow the curve of the later frame...