I was wondering that too. And what other equipment to mount the guns if any?
"Gun" - Singular. The difference in armament was 3 x .50 cal and one .30 cal or 4 x .50 cal. so one .30 cal was replaced with a .50 cal.
The .50 cal had 200 rounds. the .30 cal had 600 rounds. The weight of the ammunition would vary depending on what type of round was used, but generally a .50 cartridge is 4-5 times the weight of a .30 cal cartridge.
A .50 API cartridge weighed 114 grams, so 200 rounds would weigh roughly 25 kilos with belt links. 600 rounds of .30 cal AP would weigh approximately 20 kg with links.