I have been seeking examples of the above, only finding streamlined equipment. Heavyweight were off the menu from the start?
When Amtrak went inspecting existing passenger cars for possible purchase, the priority was:
Modeling BNSF and Milwaukee Road in SW Wisconsin
The railroads had gone through a large passenger train reduction in the decade of 1955-1965. Almost all heavyweights other than some in commuter service met the torch and a lot of the pre-WWII lighweights followed. When Amtrak went car shopping there were almost no heavyweights for consideration, and I would say none went to Amtrak.
So, I did a quick thumb-through of Craig Anderson's Amtrak 1978-1979 Annual.
Three heavyweights (RPO):
1800, ex-PC 6523
1801, ex-PC 6536
1802, ex-PC 6546
1801 and 1802 never got their Amtrak numbers. All three built by PRR in 1907.
I know I'M surprised!
Ed