The Lionel 2328 Burlington GP-7 was offered in 1955 and 1956. This is one of the most common of the Lionel geeps.
There are no variations of the 2328.
The aluminum paint Lionel used in the postwar period is water based, and cannot be cleaned. A 2328 Burlington like the one shown above will sell for $50-70 because the paint is faded. An unfaded and uncleaned loco will sell for 5-8 times as much.