Here's some information on taking your existing transmission to bits
http://www.peachparts.com/shopforum/diesel-discussion/304903-722-118-automatic-transmission-rebuild-monster-diy.html
I reckon you've got a 722.118.
Changing just the front pump and replacing the torque converter sounds like it might be a good fix.
However, you might also have worn splined shafts - see thread link above for more information - in which case you either need to find a replacement 722.118 or a different 722.1 for parts.
Fitting a 722.1 transmission not designed for your car will cause difficulties such as shifting points, throttle linkages, and vacuum system.
If you want to see which transmissions (say a 722.3) that will fit your car I might have the information you need here
http://www.peachparts.com/shopforum/general-information/311136-fsm-epc-data-%3D-chassis-model-transmission-drive-train-information.html