Rearend gear selection

I would say 3.55 or EVEN a 3.91. The 273 is a great little engine. It's exactly that. Little. The short stroke and small cube displacement are really fighting against low end torque.

Now if you talk about stepping up to a 360, that's a horse of another color. Because of the additional stroke, the 360's best street gear IMO is a 3.23. It is a fantastic all around gear.

I don't get how anyone can recommend a converter for you. No one can possibly know what cam you have. You've not disclosed that information. Hopefully, the camshaft is a mild one, close to stock. If not, it will really be a dog with a 3.23.....and not much better with a 3.55.