>> My great-grandmother's recipe for Boston baked beans includes salt pork (fatback).<<

Bacon or bacon grease is another popular option.

>> I discovered that you do have to put some fat into baked beans to help all the flavors blend together. However, you can use vegetable oil, just stir it into the bean pot before you bake it.<<

And/or topdress it by sauteeing spices in ghee or olive oil.

Red palm oil goes great with beans, if you can find an ethical source.

>> Boston baked beans are usually seasoned with dry mustard, to offset the sweetness of the molasses and brown sugar. My great-grandmother didn't like mustard, and neither do I. Her recipe calls for ground ginger, which shifts the molasses flavor in the direction of "gingerbread", and is quite nice.<<

Other funkeners include onion (or other alliums) and asafoetida.

If you like the gingerbread effect, try making beans with garam masala. That's what I usually use for making ham-and-beans.

>> It's tastier with the salt pork (which is lightly smoked), but it works okay with vegetable oil.<<

Yeah.