You need the volume of the engine, in total with all ancillaries, such as exhausts, radiators, etc. This is usually expressed in metres or feet cubed. The engine cylinder volume won't tell you very much about how big the volume of the engine itself plus everything else that is needs to make it work. Power density is a good measure (how many HP per cubic metre) but that really doesn't start becoming a concern for most engine designers until about the 1980s. The Germans are perhaps the masters of packing the maximum horsepower into the smallest volume, with 1500+HP being packed into 3-4m^3.
As a handy guesstimate, most early tank engines would consume about 2-3m^3. Most medium sized tank engines would consume about 4-5m^3. Most large tank engines would consume anything from about 5m^3 upwards. Gas turbines in particular consume an awful lot of space inside a tank hull, not necessarily because of the engine itself but it's inlet, exhaust and heat exchanger requirements.