11.00x20 rim width.

I picked up two 20" rims from a tire shop near by on Thursday, and one is 20x7.5 and the other one is 20x7.25. the 7.5 rim is dated 7-52 while the 7.25 is dated 11-62. Is the 20.7.5 for the 11.00x20 tire. It's stamped with 12.00 tire max. I'm guessing that the 20x7.25 is for the 9.00x20 tire. Any info would br great. Thanks. The owner of this tire shop is a member of my American Legion Post. He has a couple more 20" 6 lug rims that could work on the trailers.

The early rims had a different offset as well, I beleive.

The differences could be in models. I know that the M135/211 have a standard rim width of 7.50 inches. The only difference between the two models is the offset of the hub. The M211 has an offset of 6 and 3/16th inches while the M135 has an offset of 5 and 1/8th, I believe.
The rim that is dated from 1962 and is 7.25 inches wide is from a M35. I do not know the offset for those rigs. Measure the rims and see what you have. I am sure the offset info for the M35 rim would be found in the Deuce forum.
I am basing that off of the 1962 date tag since the M135/211 were stopped being produced in 1955/56.

Section8 is correct that the only difference in the M135 and M211 rims is the offset. You cannot use the M135 rims for dual wheels. On the M135 the rear hubs are flipped. The rims are the same 7.50" width for the 9:00 x 20 and the 11:00 x 20 tires. The M211 rims will work on an M35A2 ans vice-versa. They will also work on the M105 and M200 trailers and vice-versa. You could use M135 rims on a M105 trailer if the tire will clear the fender. I have had M135 rims on the front of an M211 deuce just to avoid the tire changing.
Regards Martin Sacks

Here's a dump question, Do you measure the inside of the rim (lug face) to where it makes contact with the rim (tire lip)?

Back spacing is measured typically from the hub face(point of contact with brake drum) to the outer lip of the rim where the tire seats.
Easiest way to measure your back spacing is to place the rim, with out tire on, flat on a level surface. Hub facing up.
Measure with your tape through the centre hole from the floor, level surface, to the inside of the hub face where it would make contact with the brake drum. This is your back spacing, as I am aware of.
Not a dumb question at all. Till couple years ago I didn't have a clue either.
Always good to learn new things. I am always finding something new that I didn't know on this site.