Take the 4x20mm loadout.
That's why it's 20 ENY.
There is a reason they moved from .303 rifle calibers on up to cannons. The rifle calibers were just too ineffective.
For basic AH purposes, don't forget that the guns' kinetic impact diminishes over distance quite drastically. For the .303s on the hurricane you can make quite short work of even the toughest planes, but you have to get in CLOSE. 150 yards close. Where .50cal work very well at 300 yards, the .303s are already losing a lot of their punch. Not to mention you need to get as many on target in the same spot as possible, that means the closer you get the less dispersion you get, and you actually damage the plane.
Further, if you fire from a longer distance, you run a greater chance of raking the plane from stem to stern. With .303s this does almost nothing.
I got 8 kills defending a base from a CV capture attempt once, killed F6Fs, FM2s, F4us, SBDs, etc, all without reloading in a hurricane mk.1 with the 8x .303 loadout. I did this by getting in close (150 or less if possible) and firing a good solid 1 or 2 second burst in the same spot.
I hope this VERY general list of comments helps you out. Other than this, you really should just take the 20mms.
P.S. With the .303s it should go without saying, but I'll say it: Set them ALL to the same convergence, and shoot AT that convergence. You need EVERY bullet to hit in the same spot. You can't set convergence to 600, then hit the left and right wings of your target separately... If all the rounds hit on one wing it might be just enought to take it off, but if half hits each wing it's still able to fly off with both wings intact. Set convergence to NO MORE than 200 yards (I strongly suggest 150) and maneuver for kill shots that get you TO that convergence distance. Don't shoot at 300. Get to 150 and shoot at 150. It makes a major difference with .303s.