I took the measurements, but my digital camera batteries discharged and I was not able to take photos. I may take some tomorrow, weather permitting.
There are four panels per side, eight total. All panels are 2cm thick and 61cm tall. Five of the panels are identical, three of these panels are on the left side and the other two are on the right side. The panels overlap by varying amounts.
Starting with the left side panels, the first three are 75cm wide. The last panel (rear most) is 62cm wide at the top and 49cm wide at the bottom with a cut out along the back edge.
The forward most right side panel is 73cm wide at the top and 68 cm wide at the bottom. It has a pair of cut outs along the forward edge. The next two panels are identical and are 75cm wide. They are the exact same ones as the left side forward three panels.
The right side rear most panel is exactly the same as the left rear panel. Same part number and fittings.
I have never crewed an M113A3 so I do not know if the panels were ever removed by the crews. The mounting rails are bolted on with some heavy duty hardware and removal looks to be quite a chore. I will let you draw your own conclusion since no matter what I state, some sharpshooter will go out of his way to prove me wrong.
I have three M113A3s and they all have the same spall panels. I am not an M113A3 expert nor do I pretend to be so this all I care to know about this subject.