Hi, Welcome to JustAnswer. I am a licensed veterinarian and I'm here to help you. First of all. . .congratulations to you and to Simba!
Halitosis can come from peridontal disease of course, but can also be due to tonsillitis, and gastrointestinal problems. Other than the halitosis, does Simba have any other signs, like intermittent vomiting, diarrhea, coughing or sneezing?
The diet you describe does sound tastey but doesn't supply a balanced diet particularly for calcium and phosphorous which can lead to bone and tooth loss. An easy rule of thumb is to feed 90% of his daily calories in a high quality dog food like Royal Canin and 10% in the supplemental food. This would insure that he is getting a balanced diet in everything he needs.
However, unless Simba was eating a diet low in calcium before, I'm sure that this is not the cause of his halitosis.
When you say "fresh meat or poultry" do you mean raw? The bacteria that can be on raw meat could have infected his stomach and upper intestines and be causing the smell even tho' he is not overtly vomiting.
I'll be online off and on today, so I'll keep checking back. Dr. Barbara