the 6.2 and 6.5 are mostly identical you would just be making room for the turbo. things to make it not start could be anything from, head gasket, cracked head, cracked block, broken crank, broken cam, ran out of fuel, air pocket in fuel system caused by heat, fuel pump could have gone bad & filled engine base with diesel and caused the overheat? the list is limitless without seeing it. Go look at it and crank it over and watch the coolant in the radiator and look for bubbles, check fluids and there level, use zipo type lighter on dipstick tip after pulling to check for water or fuel in oil(water will cause sparkles in flame and fuel will cause it to ignite quickly) if all appears good, have someone crank it over and spray a little starting fluid and see if it hits off(just a little and only while it is cranking) Could also pull fuse or disable glow plugs to be safe. Good Luck
