how to check ignition timing with COP system?

I just checked with Haynes... all they have to say is that the ignition timing cannot be adjusted on the late model 4.6 engines, but they do not say HOW to check the ignition timing. Just because you cannot adjust it doesn't mean you should not be able to check it. I also read an article in a Mustang magazine about how some guys swapped a Steeda timing adjuster onto a late model Stang, but then questioned whether or not the timing was accurate according to the Steeda markings, especially since Steeda said that it could be a degree or so off... but they offered no way of checking the actual ignition timing to see what was truly going on. So will this have to be a guessing game? If you swap on a Steeda ignition timing adjuster, you'll never really know how much you are advancing the timing beyond the true stock setting since the Steeda bracket may be off by a few degrees... unless you can measure the true timing. I can see a situation where a Steeda kit may be 4 degrees retarded (because the bracket is slightly bent, whatever) with respect to it's readings, so when a user goes to advance the kit by 4 degrees verses the stock setting, they will actually just be setting it back to where it was originally... and thus no improvement and a waste of time and money. Of course you could always advance the timing until pinging is detected with 93 octane, regardless of what that timing advance reading is (and then back off of course), but it would still be nice to know exactly how much you are advancing past stock. So... hopefully there is a way to pull out the old timing light and take some readings, even on the new COP ignition system. Thanks in advance.