power steering help please

[acl]

This will be long, I'm sorry. I am atempting to put power steering on a 68. I have put on a used steering box as well as 5 p/s pumps. They all will not stop whining and is not smooth steering when driving. I have put on a second used p/s box with the same results. I have had fluid "foam" out of the top of the pump cap 2 different times (never seen that before). I am lost. If a new box will fix this I will spend the $250.00 but I would like some opinions before I drop that much. I have primed the pump (turn w/fluid before belt is installed) New hoses no crimps. Any help. If I had this much prob with my first truck i might not be working on the second one. Thanks Gary