Check with Dan Jones at broncoconnection.net.I bought a complete setup last year from him and I mean complete,all vacuum lines and cooler lines,even had the inspection cover.Decent price considering these things are rare.Good luck and ask questions.Good man to deal with.
The only limitation on choice of A/Ts is the availability of an adapter and output shaft to match the D-20.I read and hear about AODs being used a lot and C-6s.I havent seen an electronic yet but am sure someone has done that swap too.
Got a complete c-4 dana 20 setup. including all the brackets,linkages, column etc. Basically a drop in. I never drove the EB it came out of so I cannot say how it worked but was told it worked good. Complete setup $500. U pay the shipping.