I won't discuss the 101 or the 101A1 trailer but instead will work with the A2 and A3.
A2 and A3 use hydraulic surge brakes and has two handles mounted on the front of the cargo box for parking brakes.
The A2 uses a straight axle tube with 5 leaf springs, CUCV wheels and tires, and the box is 46" between wheel wells. The frame is listed as being 3", but in the 100 or so trailers I've observed, I've only seen two that were not up-graded to the 4 inch frame.
The A3 uses a stepped axle which rides 5-6 inches higher than the straight tube axle of the A2. The stepped axle is also wider by 10". The A3 trailer frame is 4" and uses a 6 leaf spring pack. The A3 uses the 12 bolt HMWWV wheel with radial tire, though some have been observed with 8 bolt wheels and the old HMWWV bias belted tires. The cargo box on the A3 has lifting eyes on all four corners and reinforcement panels welded on both inside and out side of the box. The width between wheel wells is 55". There also are doublers welded on the bed top rails so that the bed won't cave in when being lifted. The fenders on the A3 trailers completely cover the tires.
There are numerous combos floating around, but the stepped axle, HMWWV tires and wheels are usually A3 trailers no matter what box is mounted.