So since they used the larger sector shaft on the 73 power steering, would you be able to use a manual box with the large sector shaft? I found one cheap here at a car show.
If you read the end of the article I posted above it says that the clocking on the pitman arms is different for the different models. Which would mean that using a C body or van box in an A with an A-body pitman could mean grinding a new master spline to re-clock the pitman arm.