The F6F 5N and the SB2C Helldiver
F6F 5N-Another improvement in the F6F-5 was the availability of more potent armament than the standard six .50 in (12.7 mm) machine guns. Trials with cannon-armed Hellcats were not followed up by a production version; although all F6F-5s could carry an armament mix of a pair of 20 mm (.79 in) Hispano cannon, one mounted in each of the inboard gun bays, with a minimum of 220 rpg, along with two pairs of .50 in (12.7 mm) machine guns, with 400 rpg, this configuration was only used on many later F6F-5N night fighters.[17]
Yes cannon armed hellcats were not followed by a production version but since they could be used on all hellcats its an option.
Both of these aircraft aren't a must have but would be a good addition.