[massey478]

For the timing, I rotate the distributor both ways, retard and advance with the motor idling. I rotate it retard until the motor sounds like it is starting to labor, then rotate it advance until the motor starts to 'flutter'. I back it away from the flutter setting until it just starts to run smooth and does not kick back at the starter when cranking which is a good place to start finer tuning as you drive it. Listen for pinging and do not set it so that persists more than a bit off the idle on acceleration if you hear it at all. Gasoline nowadays with the added alcohol will tolerate more advance without pinging. I bet you will find the motor freeing up a good bit from the cookie cutter factory timing light setting. When you are happy with it you can then put a light on it if you wish so you know where the setting is you like the best.
The 478 in my Massey 1100 seems happiest when the jet sizes cause just a bit of black smoke when under light load. Under really heavy load at night I get a 4" cone of blue fire out the exhaust stacks with a circular shock ring showing just at the top of the pipes. You will never see that on a truck because the tractor has vertical headers and short collector pipes; the longer truck exhaust system will burn it up before it gets to the end of the system. Because it is happy this way, the MSD system keeps the plugs cleaned up much better than the stock system. With the MSD you also can open up plug gap to around .050" or a bit more to create even better ignition of the fuel charge. For a truck you probably will not want to set it that rich because the truck motor is not running at 50 to 60% + of the rated HP or more all of the time.