If the genetics aren't there it won't matter what you feed, your fish will never grow a large kok.
Further more; feeding a diet such as "lots of fat and protein rich foods" will only cause your fish to die prematurely from fat deposition in & around its organs.
And no, you should not feed beefheart to a FH.
Dr. Peter Burgess MSc, Ph.D.,of the Aquarium Advisory Service in England, is not only an experienced aquarium hobbyist, but also a scientist that specializes in the health & disease in fish. He has written over 300 articles and five books on fish health and is a visiting lecturer in Aquarium Sciences and Conservation at Plymouth University, where he works with the University of Plymouth training students in scientific research. Among his other positions, Dr. Burgess is a senior consultant to the Mars FishCare business and regularly runs fish health & husbandry courses for aquarists, fish scientists and vets. He's also a regular contributor & Fish Health consultant for the Practical Fishkeeping Magazine, as well as other magazines devoted to the fish keeping hobby.
Below is an excerpt from the Practical Fishkeeping Magazine titled;
Liver Damage and Red Meats,
"The routine of feeding beef heart and other red meats to Cichlids can ultimately give rise to health problems. Poultry meat is also suspect. Red meats, including lean meats such as beef heart, contain the wrong sorts of fats - these harden within the cold-blooded fish, leading to blockages and fatty deposits around the liver.
Also, the relative proportions of amino acids within the mammalian proteins are different to those required by fish. Hence, feeding red meats will cause the cichlid to excrete more nitrogenous (ammonia) wastes, thereby placing an extra burden on the biological filter."