ironman_gq
not sure about the swap specifics but I can tell you that the th400 is a LOT stronger than the 700r4. The 700r4 also runs a little warm so a large cooler is necessary if you dont have one. a shift kit will also help it last. If you build the tranny right it should be just as durable as your th400. Have you considered finding a 4l60 tranny? Its an updated version of the 700r4 and should be somewhat stronger.
