Assuming LLX3 ECM and CDANM4 strategy, here are the stock spark tables. The lowest spark value for a given RPM and Load point are selected among the three tables. Then this value is modified using inputs such as ECT retard, ACT retard, KR retard/adder, IMRC adder, etc.
Three tests that can help you definitively determine if there is a blown head gasket and/or locate the cause of your issue: cooling system pressure test, engine block test and/or leak-down test. These will give you much more useful information than a compression test.
I know this is not the proper place to post this, but since they're only applicable to 94'-98' SN95s it seems apt. I found this listing on OfferUp for anyone looking for a set. Looks to be actual SVO skirts and decent condition too! No matching Borla exhaust though.
1994-1998 Mustang SVO side...
KOEO = Key On, Engine Off. You can try to depress the schrader valve on the fuel rail shortly after doing so. If no fuel spurts out, then you've more than likely found your issue. But a fuel system pressure test is recommended rather than throwing random guesses and parts at the car.
Just to...
Do you have before and after dyno sheets? I'm interested in the mid-rpm gains with that setup. Did you pulley the T-Trim for max blower rpm with the wastegate?
If you can, pressure test the fuel system at the schrader valve (fuel rail). Sounds like a fuel pump issue to me. Can you hear the fuel pump prime when during KOEO?