Easy conversion, especially since you bought a tranny with the same shifter setup. No mods of the tunnel are required regardless, as long as you keep your current shifter.

Complete list of parts required:

That tranny you bought
The crossmember and mount from an OD setup
The driveshaft from an OD setup. Check its dimensions before you pull your old tranny!
The speedometer cable from either an OD or Automatic vehicle
Wires, a switch, and preferably, a relay.

That's it. Assemble those parts, and you'll be running in a day.