[dsraven]

possibly modifying an old style column shifter, as LG says, would be easier, look period correct, keep a flat floor that is easier to place carpet over (if thats the plan), and keep the centre area of the floor clear for the ride a long. the detents would need to be re-made for the larger number of gears but I am sure some research would bring up fixes for that since a lot of old cars are running the same kind of driveline as we do with old trucks.
if a little more updated looking column would be ok you could try something from the mid '80's where they started using the 4 spd auto. maybe an astro van or something. the shifter tube could possibly be shortened to be above the floor, like LG suggests. the shift indicator isn't on the column though, if I remember correctly.