I'll have to look up the details, but I believe Margus showed up at SMU to train with their track and field coach and on a whim he tried out for the football team. Something like that.
He's listed at 295# on ESPN currently and if he can still keep his speed and athleticism, all he has to do is put those special tools together on the football field this season.
And Ngata IMO wouldn't embarrass himself as a 43 DE, but I don't think he would be exceptional at the position either. I see him as strictly an interior guy.