You need the bell off a 6-cylinder 'glide. It's no easy swap either, the converter has to be dissassembled to get it off, and the pump is in the bell that you are changing. Take it to a transmission shop to get it done if you're not familiar with antique automatics.
Speaking as one with too much experience with these old 'glides, I recommend that you fix your clutch. You will be disappointed in the car with a Powerslide. It will be easier and quicker to swap in a V8 with a modern 3-speed auto than monkeying around with the 2-speed, especially if you're doing an open drive conversion anyway.