Here’s the document, from the Mustang6G.com forums:
As you can see under the “Make, Car Line, Series, Body Type” section of the decoder, the 2021 model year lineup for the Mustang will include the regular GT coupe and convertible, the base coupe and convertible, and then a GT500 trim and a new Mach 1 trim.
Based on that lineup, it would seem the current Bullitt and GT350 are getting cut for 2021. Since that leaves the one 5.2-liter V8 listed on the document to the GT500, it’s safe to assume the Mach 1 will get a tuned version of the 5.0-liter.
Of course, there are no power figures on the doc yet, which means some this is possibly subject to change still, especially with how unpredictable the world is being at the moment.
The last time the “Mach 1” name was used was with the fourth-gen Mustang, but it first showed up for the 1969 model year on the first-gen pony car. It’s supposed to be a V8 performance model just above the GT trim, though it was briefly sold with a V6 in the 1970s. But we don’t have to talk about that car.
Now I’m just curious what a modern Mach 1 package is going to look like. I worry they may be too conservative with it.