I want to ultimately make a variant Portable Wargame (Bob Cordery) that covers the Classical Age. I think a good place to start would be the Dark Ages. The reason is that there are fewer troop types and therefore fewer options to deal with. Combat is a real slog in the truest sense of the word. Most of the rules will still hold true. The troops will be different.
Warbands are something that can easily be dealt with. They are potentially powerful, fast moving units that will quickly lose when things go badly for them. Therefore, the strength should be 3. Movement can be 2, like most other infantry. However, they may move a 3rd space if that move would bring them into close combat. They have no missile ability. They normally hit on a 5 or more in close combat but any combat in which they moved into contact, including followups, they get +1 to hit.
Shield-wall troops are the backbone of many armies. They have a strength of 4 and can move 2 spaces per turn. They have no missile ability. They hit on a 5 or more in close combat. They count as being in cover when attacked from the front by missile troops.
Skirmishers have a strength of 2 and can move 2 spaces per turn. They have a shooting range of 3 and hit on a 5 or more with missile combat. They hit on a 6 in close combat. If hit in close combat they must always take the retreat option if available.
Heavy cavalry have a strength of 3 and can move 3 spaces. They have no missile ability and can hit in close combat on a 4 or more.
Light cavalry have a strength of 3 and can move 3 spaces. They may be armed with javelins, hitting on a 5 or more in with missile combat with a shooting range of 2. They hit on a 6 in close combat. They may have no missile ability and hit in close combat on a 5 or more.
Instead of spelling it out per unit, I could outline abilities like “Shieldwall” and “Barbarian Charge” for the extra abilities.
I have not tested any of this so some of the units may be too weak/powerful.