I'd use the straight up gears. Ford used the retarded timing deal as a stop-gap thing to battle the federally mandated emissions standards. The straight up gears should result in improved efficiency...

As for jetting,,,, I've never tried to use that small of a carb on a 460....How do the plugs look now, and what is the engine in, and how is it driven???? Would seem a 600 may have a tendency to lean out a bit with any heavy running with a 460.....