Need advice for diff for 65 Dart factory hi-po 273.

The rear end is whining on my just bought 1965 Dart with the factory hi-po 10.5:1 273 4bbl 4-sp set up with a 7.25 rear end. The tires are 205/70 R14s.

I'd like a 8.75 but it will be $$$ and time. Maybe some day, but for now I'm thinking to just keep the stock diff. It lasted 50+ years and I won't be beating on the car and way cheaper. Am I just wrong about this. Did a quick search and A body 8.75 look to be as rare as hen's teeth and I really want to return this car back to as original as I can with some modern upgrades.

The question is what gears should I order for it? The car won't be raced, and I'd like to be able to drive on freeway without winding it up with nice mid-range acceleration for merging or passing.

What was the most usual gear ratio for these out of the factory?