Conversion, to duramax would be nice. As for the floor (hump), a nice removable panel held in w/aircraft fasteners (1/2 turn type) would be ideal way to get that allison to work.

I know my 99 is about 800+ lbs heavier than the newer burbs, guessing it's the chassis and drivetrain.

Yes, I'd buy another newer burb if it came w/diesel.