I got the seals and installed them. They work fine and I no longer leave a trail like a slug!
When I checked Rock Auto it seemed that the size of the Pittman arm seal was describing the sector seal. I guess if I had ordered them both I would have got what I needed.
In retrospect I should have just pulled the Pittman arm and replaced the seal on the car. Apart from painting it when it was out I don't think I gained much because I don't think the top seal was leaking anyway.
Regardless, Rock seems like a great resource.