Assuming an open driveline,
Whether you try to use a Muncie, Borg Warner or Saginaw, you are going to have the same amount of work. The early T10's had the corse tailshaft splines, so if the length of the tranny is correct, then it would be the closest thing to a direct swap you are going to get for your application. You may need to change the clutch disc also, depending on what tranny you end up using. The change to a floor shifter is the same for all of them, basically. Most of these 4 spds had the shifter mounted on the tailshaft, which may present a problem with a bench seat?? I believe Patricks has a shifter that is designed to work with the Saginaw and stock bench seat.