I'm not sure, but I don't think Amtrak acquired any of the UP dome diners. They were expensive to operate. Even UP had stopped using them in 1970. I don't think Amtrak picked up all the many of the UP domes of any type (they had Dome-Lounges, Dome-Coaches, as well as the diners. Though they resembled Budd domes, they were ACFs). A lot went to the the Auto-Train (which was NOT an Amtrak operation then), another bunch of dome-coaches went to the Alaska Railroad, where they still run.
The Amtrak CZ did operate with 2 Superliner diners during the mid-80s through Colorado, I used it. I think one was the diner off the Desert Wind which they operated through for awhile instead of turning it in Salt Lake. Of course, was cut off in Salt Lake City and went to LA.
Pre-Superliner, there was no Amtrak CZ, which started in 1983. Prior to that, it was the San Francisco Zephyr which operated via Wyoming and Ogden, although in later years, it did go from Ogden to Salt Lake and went west via the old WP south of the lake instead of the Lucin Cutoff. I think it was because the flooding problems they were having on the Lucin Cutoff in the early 80s.