Having gotten my book this morning, I started correlating my research on the Cossack Rebellions with the rules, and it looks to actually match up fairly easily - I can make the Polish force entirely using the rules as written, and the Cossack force only requires a few minor tweaks from the Polish list.
According to wikipedia (cross-referenced with a machine-translation of Polish wikipedia), the armies are:
POLES: 12,255 pancerni cavalry; 2,589 hussars; 2,050 other cavalry (German-style "rajtars"); 500 arquebusiers; 960 Tatars; 1,550 Lithuanian cavalry; 2,790 Hungarian-style infantry; 8,900 German-style infantry, 2000 dragoons.
COSSACKS: 40,000 Cossacks (mostly on foot); 40,000-60,000 peasants; 30,000 Tatars
To keep things reasonable on the table-top, my goal is to collect both armies at 1:400 scale. With the necessary rounding to meet the minimum unit-size requirements (as well as combining similar units, i.e. Tatars/Lithuanians and reiters/aquebusiers), I end up with the following:
Polish-Lithuanian Rzeczpospolita
General: Jan II Kazimierz
Jeremi "Cossack's Fear" WIsniowiecki's Battalia (Left Wing)
5 squadrons Pancerni
1 squadron Lithuanian Tatars
Mikolai "Bearpaw" Potocki's Battalia (Center)
3 units German Musketeers
1 unit Hungarian Infantry
1 unit Dragoons
2 squadrons Winged Hussars
1 squadron Rajtars
Stanislaw "no nickname" Lanckorowski (Right Wing)
8 squadrons Levy Cavalry
2 units Levy Infantry
Cossack/Ukrainian Uprising
General: Bohdan Khmelnytsky
Filon Dzhalali's Battalia (Right Wing)
3 units of Cossack Infantry (counts as Hungarian Infantry, but may skirmish for free)
2 units Peasants (count as Levy Infantry)
1 squadron Cossack Cavalry
Ivan Bohun's Battalia (Center)
2 units Cossack Infantry (counts as Hungarian Infantry, but may skirmish for free)
1 unit Cossack Pike (counts as Scottish Pike from the Montrose list)
5 units Peasants (count as Levy Infantry)
2 squadron Cossack Cavalry
Matvii Hladky's Battalia (Left Wing)
3 units of Cossack Infantry (counts as Hungarian Infantry, but may skirmish for free)
2 units Peasants (count as Levy Infantry)
1 squadron Cossack Cavalry
Islam III Giray's Crimeans (further Left)
12 squadrons of Tatars (Mercenaries at -2 points per unit)
The only thing left is artillery. I can't find any hard numbers for ordnance in either army, so the best option is probably just to add Medium Guns to the Polish army, and Light Guns to the Cossack army, until the two armies are equal in points.
Any thoughts?

