A Corvair box ... was designed for a light, rear engine car. A car without very much weight on the front wheels. Mustang and Vega steering boxes came out in production after the Corvairs and are designed for heavier vehicles with engines in the front of the vehicle. They are much better boxes for a 2200 lbs. and up vehicle IMHO.
I have a original GM made Vega box in my 32 Ford roadster. I have driven it 50 plus thousand miles and the Vega box works great. It is set up in a cross steer method. On my current project, I went with the newer style Uni-Steer rack ... a unit designed especially for early hot rods with engines in the front.
It is a half rack, in reality. I like it and the way it drives.
Go here ... for their internet page