A close friend of mine stayed in California for some years and she is continually going on about London Broil. I have searched and searched and I believe that London Broil is the same as our Brisket or Rib Roast. Brisket is a cheaper cut of meat, but with long slow cooking it is one of the best tasting beefs you will ever have. I marinade mine for a few hours, if you are organised, overnight - there's no written down rules to the marinade, I use mustard, garlic, mushroom sauce, horseradish, red wine and whatever I have that's appropriate. After a few hours I preheat my slo-cooker with a little water in the bottom, put in the meat and cook on lo for 5 - 8 hours depending on the weight of the beef. When cooked to your liking, drain off the marinade through a sieve and use to make your gravy.
I hope this helps, in the meantime I'll keep looking and see if there's a proper menu.
My friend said it was popular for BBQing, the hostess must have pre-cooked it.