The way that Chrysler set them up has always been correct, and the fix for a GM with poor cruise performance, or poor fuel economy, has always been to remove the vacuum hose from the manifold source, and attach it to a ported source. If this setup does not work on your application, there is a problem with the way it was set up in the first place. Another feature of the Chrysler distributor that has made an appearance on GM distributors, is the adjustable vacuum advance. If the engine has too much advance during part-throttle cruise, then the vacuum advance needs to be either slowed down (via more spring tension in the can), or limited (generally by using a different can, with less advance available). Vacuum has been ported on Chrysler for a long time, and not just since the "smog era". There is a reason for this, and it had nothing to do with emissions. It was always about fuel economy and driveability. If you need more initial advance, then dial it in on the distributor body, and not in the vacuum advance. The mechanical timing curve is always going to need adjustment from a tame setting (factory) to a wilder one, when more performance is desired. This usually involves bringing the curve on earlier, and sometimes also involves increasing the limits. That there is a problem with too much advance, leading to detonation under light load, means that the vacuum advance needs to change, not the way it is controlled. For a time, I even used a part on my 383 that came off a Ford vehicle, or can also be found on many 80's Chrysler FWD cars. A delay valve can also be used in the vacuum line to the distributor, to stop vacuum from being applied as soon. I found it very helpful, as it helped my car live on some really crappy fuel. By the way, how is the fuel quality for these cars that are running their distributors all wrong? I have found many problems associated with poor fuel quality, though not to the extent that Chrysler feels they are. Timing a vehicle to the maximum amount possible before "kickback" is not a good idea, ever. If one is looking for the most timing their engine will tolerate, there is an old trick that has always worked. With the engine at idle, attach a vacuum gauge to the engine at the manifold, and advance timing until no increase in manifold vacuum can be achieved; then, turn the distributor back 2 inches of vacuum, and test-drive the vehicle. If the engine detonates, retard the distributor an additional 2 degrees; test-drive again, and continue to modify timing until the best balance of performance and detonation tolerance is found. If you can't seem to get the timing to a good place, it may be that you need better fuel.
