The postage dues stamps from that series come in different types:
- perf 11 or perf 11 x 10.5
- colors: carmine, scarlet, dull carmine
- wet or dry printing (perf 11 x 10.5 stamps only)
There also is a slight size difference, but that depends on the perforations. So, if you can determine the perforations, you don't have to worry about measuring for size.
The Scott US Specialized does give the plate numbers of most of the the stamps that were printed using dry printing method.
The top perfs are always 11 so you can see if the perfs in the top line up with the side of another stamp to tell if they are 10.5 or not. Once you know the perf size you can then see if if other stamps line up or not. I find this method quicker and easier than a perf gauge most of the time.