As whiteman said, I've never heard of alternate gun packages for the F4U and F6F. I think someone DID post that the Navy and Marines operating procedures allowed for varied ammunition loads, including a light package (50% ammo) and there may have been an overload configuration, but I can't remember.
The only reason the F4F has two gun packages is because our F4F is basically filling in for two models: The F4F-3 and F4F-4. Although really, the four-gun package actually makes it an FM-1, which is GM's version of the -4 (the F4F-3 would have entirely different performance characteristics due to the -4 being a heavier aircraft, as well as its reduced fuel capacity).