Add John Hem(m)ings to the list, one of Thomas Jefferson's slaves and a master craftsman who did much of the work around Monticello.

Slaves were also hired out or sometime subcontracted on their own as well.

The underground railroad interviewed its passengers very thoroughly and was selective about who rode their train, they had to be worthy of the risk. If your joiners on that church were former slaves chances are good that they were the best artisans of the period. It might be worth exploring just over the Canadian border.

A little more loosely related info; There was a TTRAG in Old Salem last year. That area was known as "the Quaker belt" in NC and was one terminus of the underground railroad. The governor had to several times send out troops to put down peace rallies and protests against the war.