Marty
The SP 6000, model #295 (powered) & 295D (unpowered) were offered from 1950 to 1954. Most of them had a silver lower band, but a few have a off white lower band. They only came in freight sets. Probably 90% of them came as a A-A, a 37956 PRR Merchandise Service boxcar, a 80982 yellow Wabash gondola and a 1235 SP caboose.
Cars were the 4 wheel, 7" tin type. Set variations were mainly the same cars, but differed in qty of track pieces, transformer and coupler type.
Here's a look at some Marx 7" tin diesels.
http://www.youtube.com/watch?v...k&feature=relmfu
Steve