Classic/Antique Car Repair: timing settings and engine idle speed, vacuum advance, aftermarket distributor

Question
I need to know the timing settings and engine idle speed for a 1968 chevrolet 327 small block out of an impala with an aftermarket HEI distributor

Answer
I can give you the specs for the original ignition system but I cannot tell you if those are going to be right for your aftermarket distributor, because the vacuum advance curve and the centrifugal advance could be very different.  If you hear pinging under moderate acceleration at 30 Mph with a warm engine and the gas you plan to use, retard the timing until the pinging just goes away.  If that makes the car too sluggish, you'd best go back to the original ignition system - the engineers who designed it for the car weren't stupid!

The idle speed depends on which transmission you have and the condition of the engine.  When new, if you have an automatic transmission, the idle speed was 550 RPM in drive, but if the engine is a bit tired, you'll probably have to set it higher than that to make it idle smoothly.

The timing spec was 4 degrees BTDC unless it is a 275 HP 327 with stick shift.  Those are set at TDC.

Dick