Buy a timing light.
Remove the vacuum advance line and set the base timing to 16* BTDC.
Rev the engine up to 3000 rpm and hold it there while verifying the timing is 36* BTDC.
Replace the vacuum line by connecting it to manifold vacuum, not ported vacuum.
Verify that the idle timing with vacuum advance connected is 31* BTDC.
Take the truck out to the nearest steep hill on a side street, stop, and then accelerate up the hill from stop while listening carefully. Verify no knocking occurs.
If knocking occurs, disconnect vacuum line again and set timing to 14* BTDC. Reconnect vacuum advance to manifold vacuum.
Adjust idle mixture screws to fastest idle, but both out the same amount from the stop.
Report back.