I have a 12 bolt from a Camaro in my 67. There are a few companies who make direct bolt in Ford 9 inch, but I feel a 12 bolt will suit you fine. If the car was a dedicated strip car, maybe a niner or a Dana 60.

Hope you have that 700R built up.

What gear?

If you go to a 12 bolt, I would buy a bare housing only with no internals, brakes or axles unless you are getting a heck of a deal on a complete axle (less than $1,000).

Housing $300
Moser axles $400
Gear and diff $800
Disk brake conversion $550 (Baer)
Proper professional set up $250-300

Rebuilt 12 bolt Axle $2300
Used 12 bolt axle, unknown condition usually $1000-1500

I like the rebuilt.