Where is the pump leaking? If it's from the front shaft, there's a lip seal there that's probably worn/deteriorated. AND, it's probably worn a groove into the shaft itself. There is a thin seal that is between the pump body casting and the reservoir. You have to remove the reservoir by tapping/removing it from the pump body, then reversing to reassemble. For the price of a reman pump, better to get one to swap out with your old one instead. Do keep the old pump in case you need to transfer any fittings, you can always turn it in for a core refund later.
Personally, I always liked those older Federal-style pumps. Especially that "torque reactive" mounting bracket they usually had back then! The later Saginaw pumps are good pumps, but I believe they have a little bit smaller displacement capacity, which might mean they need a smaller pulley for similar performance? They also had a smaller, ovoid-shaped neck on the reservoir, for quick and easy identification. Chrysler started phasing them into production in about '71?
Easiest thing to do is to replace your existing pump with one like it. Which will fit your existing brackets and such. Be sure to use ONLY power steering fluid in the system, NOT atf, from my own experiences.
CBODY67