PAM 30-60-1 Vol. 3 Pt. 1 (composite image from several pages)
The first is the M1 76 mm gun, still in the service with the Yugoslavian army in Sherman tanks as of this document's composition. According to the document, the muzzle brake was not used.
The second gun is the 90 mm M36 gun from the M47 Patton tank, also operated by Yugoslavian forces.
The 37 mm M6 gun was used on many vehicles, but the vehicle in question is the M8 Greyhound armoured car. The document mentions that it "has but a limited performance against modern tanks". Indeed, 50 mm isn't going to impress anyone in this day and age.
Just like the "S" versions of Soviet guns, the M1A1C is just the same 76 mm gun as seen earlier in the table, but mounted in a Hellcat. Unlike the Sherman variant of the weapon, the muzzle brake is still used here.
The 90 mm M3 was used on the M36 tank destroyer. The document points out that this gun cannot use 90 mm ammunition from the M36 gun, although the opposite is possible. Again, the muzzle brake has been removed in Yugoslavian service.
Last but not least is the 105 mm M2A1 howitzer, used both as towed artillery or a part of the M7 Priest.