Pitman Arm Help

So, I have seen tons of questions about this, but I need some help. I have 1973 center link and idler arm for my 1971 Demon to help with oil pan clearance. The issue I have is the manual steering box is 2537349 which I think is a earlier small selector box. That being said, I believe Rock Auto is supposed to have an adapter arm that has the spline for the small selector but the top - down taper. There is a large 1.25", and 1.1", and 1.004" spline sizes under a 1973 Duster/Dart listings. Any ideas??