Most recipes involve meat and offal from a calf, though, making sonofabitch stew something of a luxury item on the trail.
Alan Davidson's 1999 book Oxford Companion to Food specifies meats and organs from a freshly killed unweaned calf, including the brain, heart, liver, sweetbreads, tongue, pieces of tenderloin, and an item called the "marrow gut" and much Louisiana hot sauce.
Sweetbread is indeed commonly found in traditional European cookery and many books refer to the use of this ingredient, including for the preparation of stews made with offal.
A French book originally published in 1928 (Ali-Bab, an alias used by Henri Babinski: Gastronomie Pratique) refers to a recipe involving sweetbread but also the spinal marrow ("cord").
Babinski's recipe for eight guests contains the following ingredients, which cook together for about four hours at moderate heat in the oven, the excess of surfacing fat being removed before serving: Frank X. Tolbert's 1962 history of chili con carne, A Bowl of Red, discusses sonofabitch stew as well.