Someone school me on converter/pump relationship please!

I have a 9.5" 4000 stall its fine on the street. its a Dynamic converter.
I bought it from A&A best part was he said if it was to loose or tight I could call up and exchange it ( as long as I did it right away ). that was a Long time ago. not sure if they still do that. they would be the first place I called if needed a converter.