This Duster has a Mopar chrome box and mopar electronic distributor. The 440 I tried it on had the MSD which proved the timing light works I think. Still, giving another light a chance on the Duster might not hurt. I have 3 of those regular lights around here. Usually one of these cars will tune up fairly good just by ear. But this one just seems a little rough on idle and just doesn't feel quite right. It will go in gear and drive down the road, although I haven't done it with the most recent ear and guess tuning. Where it was at for the dial back light test. It seems very slow to warm up and run right with more electric choke, less electric choke, more or less vac secondary. I'm afraid the retarded timing results might somehow be real.