Rearend oil weights and MPG

What made you pick 30, and at what rpm does this come in at?
And, of course, what camshaft, more specifically do you know the ICA?
At your Scr, spark-knock should not be an issue unless the cam is really small, or the timing is coming in too fast, or your car weighs a lot more than the typical A-body, or your timing light is lying to you,or she is really really lean, or the stinking Vcan is interfering. Lol.
If you keep the 12 and 30 with no other changes, then IMO, the MSD will not change much if anything. Cramming timing at an engine solves nothing, Give her what she wants and no more. Just one degree into detonation will lose more power than 2,3 or even 4 not enough. Detonation is the engines enemy. But also IMO, 30 total is not enough power-timing.
The ECU has exactly two jobs; Job#1 is to receive the signal from the pick-up and modify it for Job #2, which is to trigger the coil to fire. It is nothing more than an interpreter and a glorified set of points. Well a bit more than nothing; there are no points to burn up and no rubbing block to wear off. If your car starts, runs, and revs to the proper shift-rpm, then it's doing it's job. I have run a 360hp 367 for several years on an old Orange box, and even now 20 years later, and 70hp more, I still have no need for a CDI MS system, altho I do run a different Amp.
IMO, your tune could just be a little better.