I bought a beautiful blue Lionel FE F3 diesel set (ABA) from a follow TCA member last year. It was made in the 1990's and was conventional with one powered A unit and railsounds II in the B unit.
I gave the set to my friend and follow forum member Dan LaPage (eingineerdan@yahoo.com). Dan installed TMCC in the A unit and built a tether to connect to the railsounds board in the B unit.
Dan either now has or is getting his Lionel Service Tech certificate. He is setting up to perform these conversions. You could contact him for advice / pricing if you like.
Joe