First off all Santa Fe lightweight/streamlined passenger equipment was solid stainless steel. They never had any red stripes.
The Super Chief, Chief, and El Capitan had round end cars till different times. The Super Chief and Chief had them till 1954. Then Santa Fe sent the round end cars to Pullman to have them turned into blunt end cars. Those lasted from 1955-1958, when they were removed from both trains, with just a regular sleeping car bringing up the rear. Here's a photo of the Super Chief from 1957 at LAUPT with a blunt end observation car: https://www.railpictures.net/viewphoto.php?id=366306
El Capitan kept the round end observation car till 1956, when the entire trainset was replaced with Hi-Level equipment.
