Hi Pepe,
Love the GTX. Your car itself should be the best answer to your questions, especially the inspection marks and finishes. LA built cars are a little different that the typical Lynch rd built cars. The most obvious being the black underside and tha they seem have less undercoating. I have a resto thread on here for my LA built 71 Duster 340.
Heres the answers that I can give you.
Gloss black, semi black, flat black, natural...?
* leaf springs & hangers & shackles. (leaf springs can be either black or natural finish, hangers and shackles should be natural)
* Dana rear end (Semi gloss black)
* Dana yoke & pinion snubber (Natural??)
* rear drums & backing plates (Drums are natural, backing plate shouls be semi gloss black)
* drive shaft (Natural)
* transmission (Bare cast iron)
* bellhousing (Bare aluminum. Should have some or all engine oversprayed)
* transmission rear cross member (Semi flat black)
* shocks (Semi flat black)
* torsion bars (gloss black with lots of drips)
Again your car should have most of the answers to your questions in regards to original finishes. Products like Evaporust are great for rust removal and bring back the natural finish to parts. Keep up the great work!