I am trying not to put the OP off. She has already stated that she is doing combo, not a totally raw diet. The cat will get most of its nutrients from the complete diet she gives it.

I want to offer her a variety that she can get from her supermarket or from a butcher.

Heart is high in taurine. Is organ meat - only feed 10%.

Therefore it does not really matter if the meat is lean or not. Skinless chicken breast is about as lean as you can get and skinless rabbit is lean too.