This "variant" is an attempt to use the best rules from the various published versions of A&A, which can then be used as a ruleset for various scenarios. Mostly these rules derive from the Revised edition.

AA Gun
AA Guns fire at individual aircraft. AA guns are destroyed when the area is captured. AA fire during round 0.
Destruction when captured is from the Iron Blitz computer game. It makes more sense than reusing them.

Aircraft Carrier
Carriers cost 16. Fighters can be built directly on carriers in adjacent sea zones.
From the Revised rules

Battleship
2 hits to sink. Repair immediately after battle. Bombards during round 0. Only 1 hit to sink if enemy has fighters and you have none.
This basically from the revised rules. However, I added the vulnerability to aircraft because battleships were otherwise more cost-effective than carriers. Also any rule that encourages combined arms is good.

Bomber

Fires during round 0 at 1 versus fighters when attacking.

Generalized from the Europe rules

Destroyer
Fights at 3. Moves 2. Costs 12. Neutralizes all submarine special abilities. No bombardment capability. Aircraft can only attack subs if a destroyer is present. (Aircraft can still hit subs when defending).
From the Revised rules.

Fighter
Costs 10. Can be built on adjacent carriers. Fires in round 0 against other planes, attacking at 1, defending at 2.
I have generalized the rule from A&A Europe to allow air to air combat.

Industrial Complex
Can only build a number of units equal to the area's value. Destroyed if the area is captured.
The rule from the revised game is most logically consistent. Destruction when captured was an optional rule in the Iron Blitz computer game.

Neutrals
Are impassable unless specified in a scenario.

Retreat
Attackers can retreat after any round, except for land units in an amphibious invasion. Defending subs can retreat after any round unless enemy destroyers are present.
Although of questionable realism, this is a fundamental part of the A&A system.

Round 0
Before regular combat or strategic bombing, round 0 combat occurs. Just like regular combat, the attacker rolls first, but losses are applied simultaneously. The following actions occur
1. Defending AA Guns fire at attacking planes
2. Attacking bombers fire at defending fighters at 1
3. Attacking fighters fire at defending fighters at 1
4. Defending fighters fire at attacking aircraft at 2
5. Battleships bombard in support of amphibious invasions at 4
6. Submarines fight at 2 unless enemy destroyers are present.
This clarifies a number of unit special abilities.

Submarine
Submarines fire during round 0, as well as normal combat. Submarines can retreat on defense or submerge in the area. Submerged subs don't prevent the loading of transports. All of the aforementioned abilities are negated by enemy destroyers. Submarines can inflict hits on ships. Subs can only be attacked by aircraft if destroyers are present (no restriction on being hit by defending aircraft).
Rather than firing first in combat,they get an additional round 0 attack. This makes subs more effective and the combat sequence more consistent.

Tanks
Tanks fight at 3 and move 2.
The revised tank rule balances the unit types better.

Technology & Events
At the end of each turn, roll for technology (or other events). Then each nation bids, with the high amount gaining technology, the ally or choosing whether the event occurs. The high bidder is out the money, but the others lose nothing.
The technology rules are too random.

Transports
Transports can carry 1 infantry and 1 other ground unit.
The revised rule encourages diverse forces.

Victory Conditions & Bidding
There are 4 types of victory conditions.

Total Victory: Play until 1 side is clearly beaten and faces eventual annihilation. Bid for additional starting units.

Specific Victory: Play until a specified victory condition is met. Bid for additional starting units.

Fixed End: Play for a specified number of turns (10 is reasonable). Count victory points at the end. Bid for victory points.

Points Victory: One side scores VP each turn. The side scoring VP wins when a specific victory level is achieved. Bid for victory level.

Victory Points are usually measured by the income value of the areas held, but in the Revised game you can use 1VP per Victory City.

Building Limitations
You can't be build new units in excess of the number of units that came with the game. You may start with more, but when destroyed they can't be replaced.

This has no precedent in any of the official versions, but it increases realism and interest.

Classic

Europe

Revised

Pacific

to be constructed