I have a Mopar Performance adjustable distributor in my 440. I've set the initial where it builds the most vacuum at idle (16* BTCD). With the 24* of built in mechanical that means I'm running 40* total advance ... too much.

I've looked at the instructions that came with the dizzy but they don't say how you adjust the total advance. I've seen pictures of what needs to be done once I get to the plate but I can't figure out how to get to it. It seems like I need to get the reluctor out to get to the plate where I adjust the mechanical. How do I do this? Or am I on the wrong path?

You're on the right path. Take two screwdrivers and carefully pry up on the bottom of the reluctor--it will slip off.

Wait---as I type this, I think you only have to remove the top plate in order to access the springs. IIRC the two torx bolts are accessable so you can adjust the amount of the openings. You want smaller openings for less centrifugal advance.
Can you see the two bolts?

Once you see how it works its easy. Also a good idea to mark the current location of the slots (they slide over one another) with a fine felt pen so you have a reference/starting point.

Thanks for the tip on marking the current position.

So I just pry on it? Eh.

Yes, careful of the reluctor teeth though--place screwdrivers BETWEEN the teeth

ALSO--there is a small retaining clip in the top of the shaft under the rotor. Down in there. I think that has to come off in order to access the adjustement plate--but I am not sure.

It's been awhile since I did mine. I can't remember if you can reach the torx screws holding the advance plate without taking it apart or not. In my case I did take it apart so I could get a better view. I wound up using less than half the mechanical advance available. I run 18* initial and 32* total on the mechanical side.

"Pry on it" for the win! I've pried on too many things over the years where that wasn't the right answer.

and you see the tiny little roll-pin that clocks the reluctor to the shaft right?

Edit: I never pulled a Mopar one apart, but if the reluctor does need to come off, make sure you have the same side facing up when you reinstall it.

I thought the adv of the new adj MP dizzys was that the reluctor didn't need to come off like their predecessors? but if so R&R the little clip under the felt in the center. Take your thin needle nose pliers and expand the ends a bit (there's not much room to do it but you do gain a bit) then grab one of the vertical ends and whip it around to the open side (to expand it further) then up and out in 1 motion then as said mark which roll pin hole is in use and pry the reluctor up w 2 of your largest screwdrivers opposite of each other. EDIT on the old ones I have someone press down on the center shaft w their thumb as I pry the reluctor up w 2 screwdrivers so the cam plate does not come up/off of the pins just the reluctor comes up as some assy's have more clearance under there than others EDIT but I am referring to the old standby's as I have not worked on (or seen) one of the new (mallory type) units

I set it at 0.012 on just one gap. I thought for sure I saw somewhere that it could be set from 0.008 to 0.018 but now I can't find it.