If I were doing something like d20 Modern, I'd... (off the top of my head):
Declare that any given level belongs to one of the pack -- so if there was a foursome representing a Smart3/Tough2/Charismatic2, I'd say that one of the pack had Smart2, one had Tough2, one had Charismatic2, and one had Smart1 -- which is as close as I can make it.
Ability scores would go something like:
Three-member pack: -2 Int, +2 Wis
Four-member pack: Normal
Five-member pack: +2 Int, -2 Wis
Six-member pack: +2 Strength, +4 Int, -2 Dex, -4 Wis
(Don't remember how far up in number they went, but I remember four or five being about normal. In general, adding members lets you do more computation and helps you in a fight on the offensive end, but there's more of you to keep track of, and you've got conflicting viewpoints that can make common sense hard -- I'm trying to remember if this held true for the math-wizard Tine who, by my thinking, would have done point buy by putting no points in Strength, and lots of points in Int and Wis (the former to get a high score, the latter to counteract the penalties).)
Facing and Reach: A Tine can occupy as many squares as it has units. It can also have up to two units fight in the same square without taking penalties for fighting in close corners.
A Tine can also deploy an individual unit away from the rest of the units. A Tine can choose to send a unit up to 30 feet away, plus (Cha-mod x5) feet. (Don't remember if this maps to the book. It seemed about right, though -- not counting the long-distance device.) If a Tine sends a unit farther than this distance, or if a unit is lost through some other circumstances, the Tine immediately takes as many negative levels as there were levels associated with that unit. If the unit is permanently lost, this is considered actual level loss (but a Tine may also gain a new unit to gain back these levels).
I dunno. That's all off the top of my head, and I don't really know how well I'm remembering the ability-mapping.