I have a 1965 barracuda it had a transmission with 2 cables and a floor shifter . I changed the transmission to a newer one , what can i do ?

You can use the original shifter [ shift knob is a black ball with s/s inserts { buttons } each side, right? ].

I have done it. I always liked the knife/through/butter feel of that shifter. I used that early cable shifter on TWO cars that had the later linkage shift.
It requires some creativity & if that is not your forte, another solution might be better.