The Mopar Perf electronic ignition kit has the "fast" advance curve in it. Normally, there's a weaker spring and a stronger spring in the distributor. So, unless anybody messed with the advance curve after Chrysler built that distributor, you've got the "performance" advance curve already.
Typically, the mechanical advance should not start until about 1000rpm or so, stock or otherwise, as you don't want any mechanical advance at or just above hot base idle. Use your stock base timing setting to start with. The "all in max" mechanical advance should be about 30 degrees (in the distributor) at about 3000rpm (about 75mph road speed on your car with a 3.23 rear axle ratio). So, if your particular vehicle has a hot base idle timing setting of 2 degrees BTDC, then than should equate to about 32 degrees BTDC total (mechanical + base timing) at about 3000rpm. The optimum is about 38 degrees total, so you should be fine in that respect using your stock base timing setting.
IF you still get a "trace rattle" when slightly accelerating at slower cruising speeds, and IF it goes away with a slight throttle increase, that's fine, even back then. BUT if it's a definite "detonation" issue (as with using 87 pump octane fuel rather than the "super unleaded" 93 pump octane fuel, THAT's a different situation! One that needs to be addressed.
The vacuum advance should be not advancing at base idle speeds. I highly suspect that it's an adjustable unit, but don't know for sure as I haven't needed to do anything to my '67 Newport 383 4bbl in that respect. Insert an Allen wrench that just fits into the nipple where the vac advance line attaches. When it bottoms out in the hole, try to gently turn it until it might index and drop into the adjustment bolt (if it has one). Then turn it about 1/2 turn clockwise to slightly increase the spring pressure against the diaphragm, to basically slightly delay the amount of vacuum needed for a given vacuum advance level. BUT use this as a last resort situation!
How much richer did the final carb calibration come out to be? Just curious. With what carb?
As to fuel octane, ethanol'd or not, the current 93 pump octane gasoline should be about 97 research octane, which the original 413 V-8s were spec'd for in 1959, were spec'd for as that's what the "Ethyl/Premium" fuels were back then. So make sure that's what you use!
The other situation is that the "cleaner" fuels don't always burn cleaner, which means they can accumulate carbon deposits in the combustion chamber easier than prior fuels might have. And nothing short of mechanical removal will fix that, but you can help it with extended driving at highway speeds for extended periods of time. The "decarb" fuel additives that claim to work quick, sometimes don't. So, no quick fix.
In the mean time, you might try a non-alcohol-based fuel treatment to raise the fuel's octane level a little. Make sure the hot base timing is set to specs and see if that helps your issue. When I put the MP electronic kit on my '67 Newport 383 4bbl, I really didn't notice any issues with clattering, but then I was using super unleaded in it, even with the 906 heads and their reduced (from the closed chamber heads that were on the motor originally) compression ratio, to about 9.2 or so. With the stock ignition, I'd get some trace clatter at WOT, but nothing cruising or accelerating.
If you get into a factory service manual, compare the total timing for the 383 2bbl motor and the 383 4bbl or 440/375 motor, you'll probably see that the 2bbl motor ends up with about 36 degrees total advance. The 383 4bbl motor will have about 31 degrees advance. This lower total was allegedly done for the law enforcement customers to be able to use lower octane fuels in those higher compression motors, but the motors were still spec'd for "premium fuel". So they could buy lesser fuel for their total fleet and not really hurt the higher compression pursuit motors. At least that's the explanation I've read. So, use your stock timing setting, but use the recommended premium-level fuel.
Just some thoughts,
CBODY67
