T'alofa SI: agree with some of your post. Though do not see too many 6'4 and 340+ Samoans going out for any kind of sports, either in America Samoa, Long beach, Carson, Oceanside or any where else (if bouncing or security special event guard is a sport...OK than). Too busy with the 40's.
An 18 year old that size (fat included) and a little motivation and better than average speed, could land a partial or full (NCCA very strict of late) scholarship at USC ( trouble times there...always wondered why the west coast teams get under the spotlight the most),, BYU or the U. Always need a guy that size just to move 2 or 3 feet on 4 or 5 line plays a game. Though hard to get special helmets to fit some of those studs.
Remember that before the white Gods arrived, Samoans & Hawaiians were somewhat lean and muscular (we know this through many ship records and explorers journals). And of course, large bone, with wide frames. Heard of the Missionary position? How about the Missionary diet, with overprocessed grains, canned meats/veggies and maybe the number one causes of future obese and health problems...white sugar & flour. This was a more Christian way to eat. Still adapted today, yes quite a few of the clan seems to be checking out early, usually a little after 60. Bad diet, to me, is the number one cause. Heart and high blood pressure seems to lead. Most all my Samoan bloods have crap diets. Even the younger jocks who should know better. Though a few in the Pro's are making changes. Three of my cousins who were in, or are now in, the NFL are trying to do this. Two of there white wifes are dumping on them all the time about that. Kind of funny watching that.
Far as cardio goes, favoring interval training, rather that marathon style cardio workouts, can insure muscle gained will be muscle kept with any fat lost program. Again, Tabata leads in my view. And maybe two to four times a week (never two days in a row) max at that. Dropping carbs goes hand in hand with this, or any other, fat reduction. Good Luck.