You asking for a Drum brake car, or a BUDD 4 piston caliper, disc brake car?
Big difference.
On a disc brake car, the ball joint is part of the steering knuckle, and big $$$$$$$ to pay, if one can be found.
On a C-body, 68 was the last year for Budd brakes.
65-73 C-bodies use the same lower ball joints for drum and single piston 69-73 disc brake spindles.
The steering arm is part of the ball joint on these too.
If you can source a set of 69-73, preferably 73 disc spindles, now would be a good time to upgrade to disc brakes.
Kevin