The original 7 1/4 rear in my 65 Barracuda Commando 273 4-speed lasted 90,000 miles and a lot of speed shifts. Even with a 4 barrel, you still only have 273 cubes (i.e., not a lot of torque). I'd just run the 7 1/4 for now. If it's in good shape it might outlast you. If not, well then you can replace it.
And that’s exactly what I’m hoping for… there really isn’t much more to do with it other than give it a fair chance… any recommendations for an ideal gear oil? Does this require any additional additives for the axle bearings or anything unique?