I already had a 273 Commando to begin with. This is how I did mine, it's a fun car to drive with this:
1970 duster
1965 - 273 commando
Cam: Comp Cams Magnum 282S - 282/282 Lift 495/495 (solid) Beehive Springs
Edelbrock D4B intake / Holley 670 Street Avenger
Pertronix Ignitor & Flame Thrower coil
Hooker Headers
2.5" Dual Exhaust / Super 44 Flowmaster
8 3/4 - 3.55 - SureGrip
727 auto / Shift Kit
10" 3000 stall converter
B&M Quicksilver Shifter
I would not go under 3.55 on the rear, but I guess it's up to how you plan to drive the car. My car likes a bit of converter since it does not put out a lot of tourqe from a stop.
Here's a video
http://youtu.be/HxSr8bkjC1s