I order all the Mustangs, SVT's, and Shelbys for the Ford dealer I work at. The latest weekly ordering commodities/constraints memo does NOT show GHIG as changing availability. That makes my 99.99% certain that GHIG is still available on non-Boss models.
Here's the only Mustang ordering restriction posted in the current week's report....
On May 10 - Scheduling Unscheduled Allocation in Week 19.
The GT Track Pkg (55R) will only be eligible to schedule on retail orders.