Mustang IIs were weird when it came to VIN coding. Even King Cobras didn't have anything in the VIN, you have to look at the buck tag on the core support to tell what trim level you're looking at for sure.
There were all sorts of weird packages too, the MPG package, the Ralleye package, the Stallion cars (which shared their appearance pack with Pintos and Mavericks), Ghia Sport, and a few others I'm forgetting. I really wish MustangII.net hadn't shut down for good and switched to being a Facebook group after being hacked, all this info was archived there. MustangII.org has some of it, but it's not nearly as complete.
I don't know if anyone still has the production numbers for sub-models like that except for probably a Marti report. If you truly want to know how rare your specific car is I don't think there's a better place to get your info from. To have that info, you'd need to order the deluxe report at $46.
My first car was a '76II, MPG, with Ghia and MPG badges. The 'MPG' came in with the 2.3L-4 and the v8 rear axle configuration. You needed a running start to make most steep hills, but it would hum along at 90mph without breaking a sweat. They truly did make all kinds of oddballs.
Mine are the trim delete stock depth bumpers
I put it together with two carriage bolts on each smoothie fiberglass bumper which I probably didn't need
The bolts were to keep foam from pushing the bumper off the frame not to hold it on
They are filled with closed cell expandable automotive grade foam and thats what holds em on.
Been good for over ten yrs at this point
They have fiberglass bumpers now of different depths at CAR