Being a somewhat private person (though not introverted) I might offer that Samoa has a great influence on me. The island folk are larger boned, wide bodied and stronger by natural selection. Do not know why, just the way it is. I myself can not take credit for any physical advantage . The whole Polynesian chain seems to have these same genetics. Not all of these folks are super sized, though much more than the law of averages would allow. Bad news....Adapting to the white man's diet has given a lot of bros more body fat than needed. 300-400lbs is always bad news, no matter how large the bone structure, for a long life.
Samoans tend towards large joints to support a larger muscle and bone frame. Which can give stronger leverage when lifting. Hip and shoulder power very noticeable. Seen one Bro (very out of shape), who had never lifted anything heavier than a 40 ounce, by choice, power up 300+ in the clean and jerk for reps. Same with 325-330 BP's first time another guy tried them. Repeating this story again, be warned: My two cousins, both seniors in high school, benched 400+. Weighted around 235 at the time. To them it was not all that. Do not see a lot of Samoan BB'ers or lifter because, frankly, they are all ready big and strong. Nothing to prove to anyone. Another reason may be, they just do not care. That may be the island way.
The only white people, as far as I know, who may match this in bone structure and strength are upper northern Europeans. Met some very impressive Swedes and Norwegians when it came to natural abilities. Just check out the strongman contest. So any Scandinavian genetics (Vikings/Norseman), in theory, could help. Scandinavian blood also runs through the lowlands like Denmark & Holland. Even Germany, Ireland (Dublin was founder by Norsemen) and Scotland for that matter. Good Luck.