There is not a lot of difference in the external look of the Th 350's, but there are some difference on the internal's. I'm not sure of the code numbers any more that is on the tag so some one else in here may know that.
The major difference is in the clutch plate stacking which is done with different piston and pressure plates.
If you have access to a couple of tranny's (and if you were going to rebuild anyway) try to get one from a 4x4 and one from a passenger car, the 4x4 should have the best clutch packs etc. and you can use the output shaft and tail shaft from the passenger car.