I have never seen a .308-specific Geissele trigger unit. There are various models from SSA, SSA-E, DMR, Match Rifle, Service Rifle, etc. They will all work with in any AR-based platform (AR-15, AR-10, LR-308, etc.).
They all interchange EXCEPT between large and small pin.Sometimes, however, milspec ammo needs a heavier hammer spring due to harder primers to ensure reliable ignition.