Wow. Never saw one of those before. Heard the name. I think he did some cars as well. It's sort of a Yenko / Doug Nash sort of operation as I recall.
The roof rack is actualy a factory option. It looks like it appeard first in 75. I have only ever seen one in person.
http://brochures.slosh.com/ is drumu site and he sometimes comes through here. I would also look on
www.73-87.com
The rear hoop was also something that is not unheard of. Now the stringers between it and the hoops I had never heard of. Looking at the above brochures and did you know in 75 rear seat shoulder belts were available. I didn't know that. I bet those stringers between the hoops was part of it.
The Drop hood I think is also a Doug Nash thing or maybe a MickeyThompson thing. Nash came up with the part time kits and after his death it was sold to Mile Marker or Nash's compnay became Mile Marker. You can still get a drop hood from Hannaman and a couple other places like US Body source. Now as a dealer option I don't know. The Wagon Wheels are also a factory option.
Now the one that really gets me here is carrier brackets on the back. The spare carier off the passengerside has been a deal option up through about 80. The late 70's are still made by Valley. The brackets are stamped steel late 70's. The brackets were a cast aluminum in the mid 70's. My buddy has a 76 that still has those brackets. Now the driverside brackets are the real mystery. I'd ask about those....never know they may be in the rafters somewhere. Those are rare from that time.
I think what you have is a very rare dealer appearence group. I doubt there were any performance improvements. All the parts I can find referenece to in the dealer option but the hood and that left hand bracket on the carriers.
Interesting find. I don't know if it makes it worth a whole lot more but definatly a neat find.