[Vespers War]

A case of taking two old weapons systems and mashing them together was the Yugoslavian SO-122. In the 1950s, Yugoslavia received 599 M4A3E4 and 1 M4A3E8 (which makes page 39 of the Soviet Combat Vehicle Handbook hilarious in hindsight). In 1956, they began looking at how to replace the 76mm gun, which was rapidly becoming obsolescent. Their solution was a number of M1931 (A-19) cannon that Yugoslavian partisans had captured from German forces during WW2 (which had in turn captured the guns during the invasion of the Soviet Union). They built a new turret and shoehorned the same 122mm gun used on the IS-2 and IS-3 heavy tanks into a Sherman. The prototype also replaced the M4's engine with the engine from the T-34-85, but this was not planned for production models in order to keep the conversion quick.

The prototype was ready by 1965. Its weight had increased to 33.5 tons, but the overall performance was similar - acceleration had dropped slightly, maximum speed increased slightly to 50 km/h, and fuel consumption was roughly halved by using the V-2R engine. 100 of these were supposed to be built, but the retirement of the M4 hull in 1966 put an end to those plans.

The SO-122 in-game:
Use the M4A3E8 on page 39 of the Soviet Combat Vehicle Handbook. Replace the 76mm with the following:

122mm A-19 (Rng 400 for all shells)
AP Dam 27, Pen 55/47/40/26
HVAP Dam 27, Pen 71/62/52/34
HE C:15 B:27, Pen 11C
HEAT C:10 B:22, Pen 42C

Ammo load should probably be around 40 shells. The tank appears to have kept both internal machine gun mounts, though they would likely have taken something like a PK/PKT rather than the M1919A4.

With their lack of armor and big, slow-firing gun (Rld 1), this falls into the "eggshell with a sledgehammer" category of armored vehicles. Working as a tank destroyer from ambush would likely be their best strategy.