Lionel did not offer any dummy units for the Preamble. There were custom made "B" units on the secondary market, and anybody could have put a shell on a dummy frame.
During the Postwar period, Lionel made single motor F3's with dummy "B" units - the Santa Fe and the Texas Special. The ones that passed through my hands ran OK.
The Postwar engines have magnetraction. I am fairly certain the Preamble has tire traction.