The H&H system has been used by many gamers to fight ancient battles. Although it was never originally intended to cover ancients a good number of people have experimented by creating the combat factors and points values for various ancient armies and pitching them against each other using H&H Medieval unchanged. Others have made special rules and adapted the basic system as required. Hex based ancient games have a good reputation. I can remember playing the hex based SPI board game 'Spartan' back in the 80's which was very popular with our group and encouraged many to up-scale to miniatures and try out ancient figure gaming for the first time.
I think that an ancient version of H&H can be developed quite easily, with very carefully constructed 'special rules' introduced which will allow the distinctive characteristics of various armies to be exhibited. This would need much research and input from experienced and knowledgeable ancient enthusiasts.
The biggest problems I find are that I don't know how you would classify, say, Roman Legionaries as opposed to Greek Hoplites, and I have no idea how to handle javelins as a ranged combat weapon.
class move H-H Char stand cost
Elite Legion's(7+) A 1 CR 5(+1) A2 4 14
Legion (7+) B 1 CR 5(+1) A2 4 13
Auxiliaries C 1 CR 3(+1) A2 4 10
Archers (7+) C 1CR 1 A1 4 8
Skirmish (7+) C 2CR 1 E2 4 7
Heavy Cavalry A 4CR 4(+1) A2 4 14
Auxiliaries Cavalry B 4CR 3(+2) A1 4 11
Skirmish Cavalry (7+)C 4CR 2 E2F 4 9
Scorpion C 1R 0 HF 3 6
Onager's c 1R 0 HF 2 6
1 -3 4
Scorpion 8+ H 11+ 2H 9+ H 11+ 2H
2 - 3 4
Onager 8+ H 11+ 2H 9+ H 11+ 2H
Legionary's both normal and Elite will throw Pilum's at attacker's and also when they charge costed at +1 point per unit
Javlins I think would be 1 hex but would make them next to useless for skirmishing so I surgets formed troops with javlin get to stand and shoot skirmishers will have 2 hex range to represent groups running forward throwing and dashing back.
I only gave the Romans +1 clash bonus as they walked methodically forward and minced where the more Barbarian tended to hit hard but not last to well in a drawn out fight