My paternal grandmother, Eunice Stewart, started baking these cakes for the Christmas Holidays around 1940. When Mom (Adell) married Dad (Alvin) in 1945, Mom started helping Eunice bake the cakes and baked them every year since until Dad died in 1998. Needless to say, we used to get lots of visits from the family around the holidays!
They are called pork cakes because, instead of using vegetable shortening, they use ground pork fat. That sounds terrible by today's standards, but remember that lard was used for cooking just about everything that was made in the South in that era. The pork fat is simply an unrendered version of lard. You'll get a funny look from the meat market manager when you ask for a pound of ground pork fat.
A better name would probably be "Preserves Cake".
We've never tried vegetable shortening because we didn't want to risk the cost of the cakes. They are expensive cakes to make. If you have already made some of the preserves during the year, it will still cost (year 2000 prices) about $50 and if you have to purchase preserves the cost is closer to $100 (if you can find the preserves).
Enjoy. And be prepared to work off the extra pounds.
Please note: I helped Mom (Adell) make the cakes, but I've never done them myself. Mom always cautioned to bake slowly. If you try to rush, the cakes will fail miserably.