Q1- Is it going to have a air lock? anti freeze movement---- engine to back of sled, ( hi spot, air bubble ) to front of tunnel, ( lo spot, will fill solid with anti freeze ) then cross pipe, to back of sled (hi spot, air bubble ) then to engine, ( lo spot ) will the t stat work? something to think about, maybe a bleed screw on each side? I would skip the factory running boards in the tunnel & add 1 or 2 rear heat exchangers & run through the new homemade running boards. Maybe a 2nd radiator & fan Build it, Enjoy , let us know,