If I remember correctly the top is plastic and lower metal. I polished the plastic on mine to reveal the gray plastic and painted the bottom black. So I believe all plastic parts were moulded gray plastic and all metal was painted black. Pic from SOR.
I think I guesstimated based on what I researched, then installed the springs and measured the pin to pin length and assumed an inch or 2 of settlement after install and use. Ended up being about what all the guidance said for shock recommended for 2” lift.
I put the same setup on my 78 a year or so ago. OME and bilsteins. I looked at the 2 threads you referenced above as well as the link in one of the threads that lists the compressed and expanded lengths of the shocks and ordered accordingly. I think I may have double checked after putting the...
Had a similar issue on my 78 with oem pump, carb, etc. ended up being a punched soft line between the hard line running along the frame rail and the filter. Happened after I bolted the filter to the mounting bracket.
Let me know if i can help. I had the same question and based on the little bit of research i did it did appear to be a US spec truck but don't take my word for it.