My suggestion for your engine. Because the 360 had an early smog curve, the first thing to do is fix reduce the iniital part of the advance curve.
What you did will be OK for a drag race only use. But shorten the total advance by using the 11 plate. That with the two primary springs you now have, should get it into the ballpark. With about 20 degrees of crank advance, work toward getting the initial closer to 15* BTC at a lower rpm and experiment with making the idle mixture richer as you do this.
Lets say the advance curve in your distributor looked like this.
View attachment 1715534795
Putting a second spring on it changed the curve to something like this.
View attachment 1715534796
But your engine doesn't want an initial timing of 2.5*
I don't know what rpm you measured 20* at.
For sake of discussion, lets say it was 1000 rpm.
View attachment 1715534797
This is why the overall advance needs to be reduced from 30 crank degrees. Even if you end up getting the initial timing down to 15* at 800 rpm, 30 in the mechanical advance is too much.
Also when you have the governers out, measure the distances between the inside stops of the slots. Knowing if they are the same or different makes it easier to set up the distributor to do what you want.
View attachment 1715534791
