When I was cutting meat in Staten Island,NY back around 1978,the customers wanted lean ground beef (sirloin) for Cannibal sandwiches. Up to that time I never heard of them.
sirloin would work quite well.
Anyway, like you mentioned, we used top sirloin steak and it was finely ground. We bought it from a butcher. We served it with onions, salt and pepper to taste and brown horseradish mustard was available if that is what you liked. I did not care for it and only ate it with the mustard. I know of nobody who got sick and the Christmas tradition continued until we sold the bar. I cannot imagine using round steak and in the picture the meat looked too much like raw hamburger. What we served looked more like a bright red liver pate. You spread it on rye bread like peanut butter.