Ed,
I have been told both ways... The Dyno shop here even told me that They themselves can unlock vinlocked xcals...
I believe that a tuner can not build a file without the "base"file first.... I was going to become a SCT dealer back in the day but the BS and all the stuff they wanted you to be "quiet" about was too underhanded for me...
I guess it is how well you know the tuner and what they are willing to do for you..
I do believe that on the v8 and v6 St the transfer functions are the same and any tuner can do mustangs and Gen 2 St's...
Again, thats only what i can hear and have been told. IT could be 100% wrong....
Todd Z