$800 rebuilds are a thing of the past.
any transmission that has been sitting for years or you don't know the history most likely needs a rebuild. Anybody that can pay good attention to details and has some tools and mechanical skills can rebuild a T350-T400. Just lay it all out on a table in the order you take it apart and put the lip seals in the correct way and also make sure the spool valves are not stuck or binding up in the valve body.
Air check the forward and reverse pistons when you get the assembly together before you assemble the whole thing.
Piece of cake