Town Car: retarding timing and Jacobs Electronics ?

[rhb1999]

Someone in my family has a '89 Lincoln Town Car w/302. Since this car uses premium gas, could I get away with retarding the timing a degree or two so it could use the mid grade or will the computer let me? Also has anyone used the Jacobs Electronics Mileage Master Kit? www.jacobselectronics.com They say it monitors engine RPM and adjusts spark intensity accordingly. Do they really help mileage on the street or are they only good for racing? I have already installed a MSD Blaster coil, Ford racing wires and Bosch platinum +4 plugs. Thanks.