So I received the above mentioned unit in decent condition a while back when trading for parts for my 440. Unbeknownst to me, it was a mechanical unit, not a vacuum advance unit. It's also set up to run with an MSD box as opposed to the Mopar ECU.
At this point, I'm trying to decide if it's worth using, or should I find a vacuum advance distributor? I know the vacuum units are better for MPGs, but honestly I'm not too worried about that. Aside from that, I've honestly never used one of these units before, so any advice you all have is appreciated.
IF the MSD distributor was something you wanted to use, then get the electronics to make it work. IF it was a "happy find", unexpected, then get something else. There are several choices for a Chrysler-type electronic ignition kit, whether from Ehrenberg on eBay, Mancini, or Mopar Performance. Used to be that the MP kit's "quick" advance curve maxed at 3000rpm, which the current ones might also do. At least the above-named vendors understand what "OEM-spec" is and means to the quality of the components.
In the "auto supply brands" realm of things, new or reman/rebuild, they will usually fit everything from the first B/RB engines in 1958 all the way to 1978, which means the advance curve will be "will work" rather than being specific to what YOUR engine started life with. Yet, the basic advance requirements of the B/RB engine will be the same all the way through. What changed was compression ratios and emissions controls related to ignition timing. Not to forget that the advance curves of the 2bbl 383s seemed to be pretty much "as desired", with total usually ending at 36-38 degrees BTDC total advance, whereas the 4bbl engines usually had less total. SO, rather than being "plug and play" (which might work decently well), you'll need to verify what is in the distributor and go from there. (as to total advance and when it happens).
Vacuum advance IS necessary for good fuel economy. Once, years ago, out '66 Newport 383 2bbl suddenly dropped to about 13mpg average, from 17mpg average for the amount of freeway driving I was doing. Everything looked good, until I put the carb on fast idle and checked the ported vacuum (it was there), but the engine rpm did not change with the vac advance line hooked up or not. So a new vac advance unit was installed and all was good again. MPG came back, too!
Users usually want a mechanical advance only distributor for full race vehicles or medium-duty truck applications. Uses where manifold vacuum is usually too low for the vac advance to really make any difference in performance. Some used them on multi-purpose vehicles, too, but with the added expense of "no mpg" to deal with as there might be a bit more prestige of having it (and being able to afford such things).
It's been predicted that fuel prices will be up for another six months. Who knows what the then-current world state will be in THEN, so it might be best to plan ahead and get a vac advance distributor now. FWIW. YOUR judgment call.
Just some thoughts,