From what can find in real-life about US MA1 Sherman OP Tanks:
The M4A1 sub-designation indicates a Sherman model manufactured with a fully cast upper hull, a standard Continental R975 radial engine, and a 75mm medium-velocity general-purpose gun. Artillery observation tanks are fitted with additional radio equipment and greatly improved optics. However, as is the case with the Sherman, this necessitates the removal of the main gun, replacing it with a dummy barrel. The Armored Field Artillery Battalion was equipped with three M4A1 in their Field Observation Sections.
And come to think about it, I don't believe the MA was used during playtesting (it has been several years since I playtested the scenario). So correction to my previous statement, NO MA, only a BMG, a CMG, and an AAMG for armament.