First of all, if you don't know what a Tercio is, click
here.
This will be, first of all, only possible with clans, because of the amount of cohesiveness you need to fight in a Tercio.
The way I would see it is, pikes, being able to stab through friendlies at point blank, makes them ideal over long spears for this formation.
Second of all, the gunners should most likely be replaced with arbalest-users or heavy crossbowmen, depending on what you prefer, longbows may also work.
Third, the "Heavy Infantry" in the Tercio, should be shielders, to protect the pikemen and crossbowmen from ranged.
This should be the end to any annoying cavalry and archers if you can get a large, decent group together.
If anyone wants to put in their 2 cents about how well it will work, or how bad it will fail.
Mods, feel free to move this if you feel it is in the wrong place.
It would be similar to this
HHHH
PPPP
RRRR
H=Heavy Infantry
P=Pikeman
R=Ranged