Howdy Cappy,
Measured an original I have, it's the side with the v-shaped braket for the tripod head. It is 22"x26.5"
Repro i have is 22"x29". 22 being the width on both these. The repro is a little taller I believe because it has the brushguard
bracket that wraps around to bolt to the upper rear side armor. Those must have been late war.