Take the onions out while still firm, and chop fine all the meats and the onion. Add enough of the broth to moisten, pack in a bowl, cover with foil that you tie down with string, put it on a rack in a deep pot, fill the pot about halfway up the bowl with boiling water, and steam for 2 hours. I don't know why you couldn't leave out the liver if you want. I liked it best sliced and browned in the frying pan, like scrapple. A pig was a much more common butcher animal than a sheep in most parts of this country, so we find much the same sort of dish made with pig parts.
Some recipes even call for just meat from neckbones.
You don't have to be a great liver fan to like scrapple with liver. You will also need grain meal and flour to thicken the scrapple. Really the cereal is whatever you like the taste and texture of, but you probably need some flour so it will slice. Boil the meats in water to cover until you can slip the meat from the bone. Non-purists often dip it in egg first, or egg and flour or cornmeal.