The part number and date codes are stamped about 24 inches from the rear joint. Here's a pic of the original from my T/A with the 2883782 number with a C 70 date code. Trans Am cars (and some others I believe) had 7260 u-joints in front and 7290 in the rear.
AMK carries a variety of plastic straps. I’m guessing you can find them elsewhere if you can figure out what they’re called.
https://www.amkproducts.com/bulk-fasteners-products/?Product_ID=13201
The 71 N-code Challenger convert should have an argent grille and argent taillight bezels. The tail panel should be body color.
Grabbed this pic from the web (ignore the “Hemi R/T” emblem)
I have a May SPD JH23H1B that came with an argent grille and tail panel. I believe the addition of the rubber bumper option on a Challenger in 71 resulted in a black grille and tail panel regardless of the performance level/engine. Also, the black 71 grille was molded black. If you have a...
That’s a 72-later E-body am/fm. I sold one a few years back for $250.
https://forum.e-bodies.org/parts-misc-for-sale/9/1972-74-e-body-amfm-radio/26360/msg300125#msg300125