The problem with one for a right hand action is the port cut out blocking the port for the opposite side. 2 piece bases would be ok.There's no such thing as a left hand scope rail, just a get a normal one. Or some 2-piece bases.
Never mind I see the Farrell bases and Nightforce ones are scalloped out on both sides of the base for either right or left.
So are the ATRS rails. They work well on LH rifles and in my opinion are superior to either Farrel which are good but very thick so your scope is in the stratosphere.
Both Farrel and NF are mild steel that is phosphated which does little for rust prevention. The ATRS rails are 416 stainless and nitrided which is far superior for rust and looks really nice.
I have them on most of my rifles along with their rings and like everyone else who has tried them will never use anything else again.