Alright here's the example. Let's say you got 130 Dwarfs (and PC's) taking on 110 Goblins.
First off I think group initiative is warranted here, as its just quite a lot easier. roll 1D4 whoever is highest their army goes first. Maybe add a few modifiers into the dice roll, for example half the armies troops are gone - 2 initiative. Have higher ground? + 1, thank kinda thing. (I would think maybe a 1D10 might be better... I'm just riffing here).
Foot Soldiers/Front Lines 95 AC 5
Archers 20 AC 6
Magic Users 15 AC 8
Foot Soldiers/Front Lines 60 AC 5
Archers 40 AC 6
Magic Users 10 AC 8
Each army unit is treated as a 3rd Level Warrior for ease of use determining the to hit number. Units are in groups of 5. Rather than use Hit Dice for each unit. Any damage that occurs is taken off the number of units rolling a 1D6.
0 1 2 3 4 5 6 7 8 9
18 17 16 15 14 13 12 11
1. Initiative determined2. Attack Roll
3. Damage 1D6 from units
Its an idea, it may not be a great idea, I have to play this out on paper and see how it goes.