I’m 6’6” 315 lbs and just bought a Muddy Magnum Pro. Apparently, the material for the leg loops aren't long enough to get down and around the crotch. It’s not so much have enough room from being too round, but rather too tall and long. Any idea of a good harness for the big and tall?

I'd maybe look at logging companys that make climbing harness's,
as I gather they can MAKE you one of any size you like
doubt it would be cheap, but would be quality and fit you right! so maybe worth it?