Heart and tongue are probably the easiest to cook as they are just muscle. In a curry or casserole you really can't overcook so long as there is sauce. Two to three hours is best.
I often make a curry with some muscle (heart, tongue or normal) and liver. Just throw in the chopped liver for the last 10-15 min then let cool. Kidney is usually cooked for as long as the steak in steak and kidney pie.
Chicken and pork are the mildest tasting liver. Beef and lamb are stronger. I don't think any need soaking
Pork is the strongest tasting kidney. I think it needs soaking. Lamb and beef are mild enough to not need soaking
Four years Primal with influences from Jaminet & Shanahan and a focus on being anti-inflammatory. Using Primal to treat CVD and prevent stents from blocking free of drugs.
Eat creatures nose-to-tail (animal, fowl, fish, crustacea, molluscs), a large variety of vegetables (raw, cooked and fermented, including safe starches), dairy (cheese & yoghurt), occasional fruit, cocoa, turmeric & red wine