The old C-4 confusion problem!
If you have a pan fill C-4, Congratulations! It is the HD version of the C-4. It has a stronger case design that has 5 seperate bolts that bolt the bell to the case, not using the front pump bolts like the case fill C-4s do. It has basically the same internals as the case fill but only has the larger bell and flywheel set up using the 11 5/16 bolt pattern convertor, same size as the AOD uses.
If you don't have the original dipstick and tube all is not lost. I think I saw a pan fill set up available from PA automatics and possibly Lokar, the street rod parts guys. The OEMs a long gone from Ford and were not as popular back in the day so junkyards may be a tough slog.
Good luck!