Distributor changes

Abodysrule said
For the 32 degrees at 2800 mechanical, I guess how that 32 is applied will depend on the build, right? This 360 mag will have a cam that isn't lopey, but somewhat aggressive I'm told (I'll see if can get the specs from the builder).

Yes it will vary a bit with cam, compression, heads etc. The 32* is at 2800 is a starting point that ought to be close.

Abodysrule said
So, as a first approximation, I have the FBO limiter plate and spring kit. Many posts I've read say throw out the heavy stock spring and put a light one in it's place. The kit comes with gold (strong), silver (medium) and black (light) springs. Good guestimate of which I might try first?

As a first approximation, run it as you bought it. Install it per instructions (with vac advance plugged).
Measure timing versus rpm from as slow as it will go to as high as you feel comfortable.
If its like the old Chrysler built ones, the curve will look something like this

Abodysrule said
Then the limiter plate slots appear to limit travel of the weight pins in both directions, not just at one end of the slot, but both, so keeps more initial timing and limits total under acceleration. Good guestimate of a first slot to try? Say I choose 16 degree slot, and the springs allow the full 16 degrees at 2800 rpm, then I add 16 by advancing the dizzy at that rpm. As you say idle is what it is after that's done, I usually set my idle at 800-900 rpm.

That's interesting. Depending on the original governor's slots begin and end, that could be so. I alsways recommend measuring the distance between the slots as well as their lengths before making any changes. Chrysler had a number of ways they could set up the curve and while it seems all those similarly stamped ought to be the same, can't be sure what you have unless you measure it.

Anyway, do not limit the timing to 32 at 2800 rpm. That's the reference point, thats all. Timing should continue to advance slowly with rpm for a few reasons.
The heavy spring is special because of the long loop. This delays engagement for X number of degrees allowing a quick advance, then a slower advance. In general Chrysler timing advances very quickly from idle to 1400-1800 rpm. Then advances slowly with increasing rpm.

The secret advantage of the heavy spring for high rpm when using electronic ignition.

Since you are begining with a MP distribiutor (or copy) you shouldn't have to mess much with the springs.
If you do, this thread has a good example of trialing different springs and making other adjustments.
https://www.forabodiesonly.com/mopar/threads/distributor-curve-help-needed.496183/

Abodysrule said
Then I do the vacuum method and figure out any vacuum can adjustment based on vacuum to get me to 50 degrees. Correct?

Yes.