The original plan for the 2mm English Civil War project was to use the One Hour Wargames rules, adapted for the purpose from the Horse and Musket chapter. However, I've discovered that this has already been done for me, with a specific rejigging of the Pike and Shot rules for the civil war. This variant adds two more unit types to the basic four unit system and a few specific rules tweaks to reflect the tactics used by the Royalist and Parliamentarian forces.
This looks really good although I think I will turn the Parliamentarian cavalry into 'lobsters' along the lines of reiters in the original rules, rather than use them as distinct from the Royalist horse. I need to check out the rules a bit more but, as you can see, I've already mocked up the basing for the six different units including (from too left going clockwise), pike and shot infantry, cavalry, 'lobsters' or trotters, dragoons, artillery and commanded shot.