What's the difference between immodium and pepto bismol (bismuth subsalicylate) in terms of anti-diarrhea? would either help with lower abdominal cramp + minor diarrhea?

Totally different: Imodium's active ingredient is loperamide, which slows down intestinal motility. Pepto-Bismol uses bismuth, which decreases secretions into the intestines. Slowing of the intestines can actually make cramping worse, and make it harder for the body to eliminate a GI infection, but may do a better job of preventing dehydration when vomiting is also present.

Imodium (loperamide) maybe: Imodium (loperamide) works by inhibiting bowel muscle action (peristalsis). Pepto Bismol works instead on the bowel lining (mucosa) by reducing secretions and by its antimicrobial effects. The Imodium (loperamide), which should be used under a doctor's supervision and for a limited period of time, can cause cramps, urinary retention, constipation and paralytic ileus. Do get a diagnosis first before starting.