Advance Curve - MSD Distributor?

[PHOENIX]

OK I got an earlier birthday present (MSD 8365).

Got it installed and truck is running and holding timing.

Idle seems a little rougher then before; idle speed currently at 780 (manual trans).

I left the (2) heavy springs in when setting the initial timing.

I then changed the setup so I had (1) heavy spring and (1) medium spring.
I drove the truck and it started running rough at around 3000 rpm and started pinging at about 3300 rpm.

I then changed the setup so I had (2) heavy springs again.
I drove the truck and it started running rough at around 3300 rpm and started pinging at about 3600 rpm.

I am guessing that I should remove the blue (21º) advance stop bushing and install the silver (25º) advance stop bushing.

Does this sound right?
See the images below from the msd instructions.





Thanks.