Just a couple comments. The old tires were measured in inches, the newer numbers are metric. So the 5.60 would be approximately 5 5/8" in cross section measurement (the width of the sidewall "bulge"). The metric equivalent would be approximately 145 (mm), use a tape measure with both systems to give you a quick reference. A 5.60 will fit on a 5.5" wide rim (measured inside the flanges just for clarification), but that will force the beads to spread out to nearly the same width as the cross section, giving the sidewalls an odd "vertical" look. A 4.5-5" wide wheel would be more appropriate for this tire size. You may want to look for a '41-48 Merc wheel, they're 15x4.5 (maybe 5" even, tougher to remember now), and have the 5.5" bolt circle, and you'll have the same center for cap mounting.

Here's a reference chart that has some of the data you might use; http://66ford.fordregistries.com/Tir...0Reference.htm