The rear is certainly the original to the car. It's correctly dated and has the 4:56 code. Mr. Guldstrand was known for fabricating his own rear disc and suspension pieces.
Here is a link to yet another CRG discussion about shocks that shows the rear of this car and it's SIX shocks(reply #8-12);
http://www.camaros.org/forum/index.php?topic=7795.0
As for the rear wheels the bolt pattern is still 5 on 4 3/4. I still remember rolling it off the truck and watching the rear wheels wobble all over the place. The previous owner had trouble getting rims that would clear the big brakes and the spacers that were there. Thus there were all sorts of spacers and washers to make something fit.
The Gledhill truck may indicate the car originally came from there but I have no evidence of that yet. I do however own several of the license plate frames. The car seems to have been ordered as a Z28 with endura bumper, spoilers,cowl hood, 4:56 gears and no radio.