3.73/3.08 = 1.20 x 40mph = 48mph

I have a 3.55 rear end in my 1954 3100 trucks. With 31.5" diameter tires and 1:1 top gear, it can cruise nicely at 60-65mph (approximately 2300-2500 RPM).

The standard 3-speed transmission would be 1:1 in 3rd gear.