Manual steering boxes are almost always small sector. I think there might have been some large sector manual boxes used in C body or vans but I can't say I've ever seen one.
You don't need "rare parts" for that car. Off the shelf Moog parts that you buy from Summit or NAPA should work just fine.
I just went to Moog's website They do not show a listing for a 383 pitman arm, Every engine but, Napa lists the same arm for all engines, however they do show a rare parts one that is WRONG, it is a LARGE sector pitman. If you have one that works great,
The one's I had were either a large sector or clocked wrong which threw the rest of the steering linkage off center.
Per Firm Feel, the BB A body pitman is different, small sector and clocked differently that the other applications. That is the case with this car as well
