You could get an entire 3rd member for the 9inch and change it out in a day in your driveway if it doesn't work with those gears. The 270 is a good engine and should be able to pull through those gears, but it won't be a stoplight racer!
Will you be able to use that granny low transmission? Does your truck have a torque tube? I'm just trying to envision the whole driveline setup.
I'm using a full floater 9 inch in my truck. I had the new hubs drilled for the 6 on 5.5 bolt pattern. I will have heavy duty 4 wheel disc brakes... 12 inch rotors that are 1.25 inches thick front and rear.
