My 2 cents worth.....
Like the built 350 / 700R4 combo. If you are prone to stomping on it once in a while, would be nice to have posi in the rear end.
You should have decent RPM at highway speeds
Pull the front axle and install - gasp - Mustang 2 style, with power rack. Gets you good suspension, fairly large disc brakes, power steering, and lowered ride height.
There are a number of AC systems out there with small condensers. Still a tight fit under 42 dash, but doable
Consider tilt steering column as stock seats have minimal adjustments
Beyond that only limits are your imagination and your pocketbook
