With veterans yet to report, Brown got the first-team snaps Monday and Polk ran with the second team.
Unlike the 5-foot-8 Lewis, Brown and Polk offer size and power.
"They're not little guys. It's been a long time since I had that many backs with size and with appreciable speed," running backs coach Ted Williams said.
Williams seemed especially enthusiastic about Brown, who at first blush looks faster and more athletic.
"He's extraordinary in that with his size, he has little-man skills," Williams said of Brown, listed at 6-0, 220 pounds. Quiet and reserved, with braided hair that spirals around his head, Brown looks as if he could plow through a linebacker. "He's strong. I can't wait to see him in pads and see how physical he's going to be."
While Brown had just three competitive carries in the last two years, Williams had an idea of what the Eagles might get when they drafted him 229th overall.
"I worked him out, I spent time with him and his family and I got to know him," Williams said. "I have a friend who lives in the town where he grew up and knew him as a child. I have a lot of faith in this person."
His time with Brown indicates that the Eagles weren't just taking a flier on him.
"This organization gave me a chance, gave me an opportunity, and I'm appreciative for it," Brown said. "That's really what I try to focus on. . . . I have to get better and show these guys that I am worthy of the last pick."
Polk has size, too, and said his preferred running style is to go right at defenders. Despite tearing the labrum in his left shoulder as a freshman, the 5-11, 222-pound back ran for more than 1,000 yards each of the last three seasons at Washington, giving him much more on-field production than Brown.
"You don't realize how big he is when you look at him on college tape until you actually grab him by the arm. He is a man," Williams said. "He is faster than he appeared to be on tape."
Each comes to the Eagles with questions that deflated his draft stock. Brown, a highly recruited high school star, transferred out of Tennessee after one season and lasted just three games at Kansas State before quitting the team. Williams said Brown is growing up.
"Of all the young kids I am coaching, he appears to be the one who has his mind focused on what he wants to get done," Williams said.
Polk has a long college resumé, but was battered by left shoulder injuries. He tore his labrum three times; twice he had surgery, and he has played with the last tear for the past year-and-a-half.
The easygoing Polk said an MRI exam might look bad, but game film will show a player who didn't miss a start.
Contact staff writer Jonathan Tamari at 215-854-5214, firstname.lastname@example.org or follow on Twitter @JonathanTamari.