The F-35B went with the external pod to make room for the lift fan, and the F-35C dropped the internal gun for more fuel.
The gun pod, when fitted, is full stealth. The other external stores racks are not.
The F-35A carries 181 rounds for its gun which is capable of firing at 3000 rounds/minute. The F-35B/C with its pod can carry 225 rounds. Whoopee!!!! The A-10 carries over 1100 rounds.