The LSD center is for off-road, yes. Unless you preload it very loose to work, it will cause more understeer. Before the 6-speed XTrac setup, Mitsubishi's factory rally cars used a Ralliart viscous coupling in the sequential 5-speeds, which was different from the Ralliart viscous coupler that Mitsubishi sold over the shelf to Evo customers. A couple of them have survived, but the whole transmission is needed to make it work.
I'd argue that the Cusco Tarmac is terrible for rallying - it's an open diff with no locking ability, after all. No locking ability in an AWD diff means it would allow one axle to spin for days while the other axle watched and laughed. Tarmac and gravel setups are typically complete opposites on the setup spectrum. Tarmac needs loose center diffs and heavier spring rates to prevent sway, gravel/snow needs tight center diffs and low spring rates.