I like the CAP idea.
Still, you could certainly retrofit a P-51 or even a P-38 to land on a carrier. There is also no reason why a P-51 could not carry a bomb or a torpedo. Here are my rules for both torpedo planes and dive bombers:
Dive Bombers
During the Combat Move phase, before you move any of your units, you may designate any number of fighters as Dive Bombers. Dive Bombers may attack in two different ways.
Tactical
Your fighter attacks on a 5 during the first round.
Strategic
Your fighter may conduct a Strategic Bombing Raid against an IC. Each fighter roles 1d6, and inflicts damage equal to half the amount on the die, rounded up. All other SBR rules applying to bombers apply to dive bombers.
*If enemy fighters are present in a territory or sea zone being attacked, fighters may not act as dive bombers in those territories.
Torpedo Bombers
During the Combat Move phase, before you move any of your units, you may designate any number of fighters as a Torpedo Plane. During the first round of combat, hits inflicted by Torpedo Planes can only be inflicted on enemy ships.
*Long Lance Torpedoes give Japanese planes a +1 for this first round strike.