TH400 has a 27-15/16" distance from face to CL of the trans mounting.
700R4 has a 23" distance from face to CL of trans mount, on typical transmissions.
You would have to move the crossmember toward the motor for it to work.
Any 700R4 prior to 1987 I would avoid like the plague, they have several weak components which were not fixed until 1987, and you can use many newer components in them that you can't in the pre-87's.
There are NO electrical sensors on 700R4's except possibly a VSS, and you can easily buy a cable setup for them as they were available from 1982-1989. The only other connector is the converter lockup, and you want that.