He just replied back and yes it seems like the previous owner did the work. Still waiting on engine info but it is converted to disk fronts and kept the original drum parts. Has 273 rear so I'm think a manual swap would also need a gear swap.I would not put a T-400 behind a factory power level T-400. They are power hungry compared to the T-350 and the T-350 is faster due to this. Seen it a zillion times.
But you are likely never to hurt the T-400 no matter how you assault it.
The kits would be the way to go unless you have an exact list of every piece and part needed to make the swap down to the thrust bearing in the crank that carry's the input shat nose. The shifter/console parts etc.
Does the kit come with a new or reman. 4 speed. Thats a huge thing. Sourcing a used box can cost more in the long run.
The car looks solid and well kept. Even money he paid $28 for it and is flipping. Just like ammo these guys are leeches.