[Captainfab]

The '68-'86 C series and '87-'91 R series steering boxes are all interchangeable. The '68-'79 steering boxes will have SAE style fittings. This is the range to look at if your pump has SAE style of fittings. As for the different ratios, I do not know of any specific applications or ways to ID one from another aside from actually turning it and checking the turns lock to lock. I believe Red Head Steering as well as AGR can set you up with a specific ratio if you want to go that route. CPP, POL also have quick ratio steering boxes.