I'm assuming the shifter was from a later Monte Carlo with 200-4R. If so, you not only need the cable bracket that goes to the pan, but also a shift cable for a TH350.
I currently have a 200-4R shifter in my car connected to a TH350. It works okay, but the gear selection is a little soft. In other words it goes into the right gears, but you don't feel a positive click.
You can purchase the new cable from RockAuto...and check out the link I sent you for Dixie.
That's where I bought the cable bracket.
You can try reusing the cable boot from the other cable. They don't supply them with a new cable.
Here's the link to the bracket.
http://www.dixierestorationdepot.com/Product/Detail.aspx?s=DM00414&d=1083&p=2