I would definitely go with the 13.5 LH piston instead of a 3 lug. There's really no use in spending more money on a 3 lug if there is no reason too. It's not like you are installing underneath a hand guard or something.
Also, a TiRant 9S is more suited for a sub compact 9mm pistol instead of a carbine anyway. You would already have the required piston.
Also, a TiRant 9S is more suited for a sub compact 9mm pistol instead of a carbine anyway. You would already have the required piston.