There isn't a seal close to the differential.
there are seals at the outer ends of the axle bells and the same seal at the front of the torque tube.
The axle needs to be disassembled to change them.
I wasn't able to find a cross reference either, but any early ford supplier has them. So pick the vendor of your choice.
They have a model A part number from memory.
Mart,
Edit B-4245-A is worth a google. One vendor sells a set of three at a good price. That vendor is 35fordtn on this forum.
50044