Is your setup a standard Prevost or has it been modified?
My 1987 8V92 model had the gearbox positioned out in the open behind the rear doors, and the exhaust from the turbo was well to the rear. Nothing was placed above the gearbox. For what it’s worth, early Prevost chassis originally had metal fan blades, which were quite heavy. A retrofit with lighter nylon or fiberglass blades was offered to reduce wear and tear on the gearbox.