If I recall, you would actually retain the bracket that connects the backdrive rod to the selector shaft on the transmission. Then you would add the lever that comes with the shifter and attach the shift cable to that. ..if that makes sense to you. Doing it that way retains the use of the stock reverse light and neutral safety switch. No wires to cut and splice. You might have to run a lead for the shift indicator light...if supplied, of course.
Did your shifter come with an instruction sheet? It should cover that information.
If not, as suggested, go to the B&M site and I'm sure they have a PDF with the instructions.