Despite what many people will tell you, Ford were not silly. There was no point at all to run conservative timing in terms of power, economy, emissions. If anything they would have done the opposite on later Scorpios as their knock/misfire detection on the BOB was incredibly advanced.

You may see gains with a little more fuel and advance, they try to run as close to stoichiometric as possible so going to an AFR of 12.5 ish on power with 2-3degs probably would still mean no det but a little more power. I suspect this is why people see gains when they install the vauxhall injectors.

Best way to tell is to do a dyno run at standard, then add 2-4 degs over the entire map and do another power run listening for det. If torque remains the same then Ford were already close to or at MBT, most modern combustion chamber designs mean the MBT is not knock limited. Running a little richer at the expense of emissions, and raising the rev limit if your still making good torque at standard limit will yield you the most noticeable gains on a standard engine.