.
I only find one picture with the USPS logo, but when it started or ended I still couldn't find the question for that answer. It's not much but I hope you enjoy it.
http://www.rrpicturearchives.net/showPicture.aspx?id=2437390
Amtrak America, 1971-Present.
MHC-1 1400 series were introduced in 1984 and MHC-2 1500 series in 1989.
There are differences between the two. The differences are the roof, trucks, doors, basically the whole car body was redesigned for the 1500 class. I seen pictures of the 1400 and 1500 worked together in the 1990s.
http://www.rrpicturearchives.net/showPicture.aspx?id=3325464
The USPS logo added on these cars are unknown to me, but I believe someone else has that answer.
I could be wrong but I believe I saw Walthers sell the MHC 1400 series a long time ago. I do know that Walthers and Kato does sell the 1500 series in Phase III and IV.
I hope this helps a bit.
Amtrak had two types of MHC cars when they were in use, the 1400 series and the 1500 series. Other than the trucks were there any differences between the cars? Weren't the 1400 series cars phased out before the MHC cars were all retired? When the the US Mail logo start appearing on the cars? Are the Con Cor cars the only models of the 1400 series and Walthers and Kato the only models of the 1500 series?
Kevin
http://chatanuga.org/RailPage.html
http://chatanuga.org/WLMR.html