The further I dig into the subject, the more sets I discover that had the 1666 and those 3 cars. Set # 1089 had the engine and cars strictly as Nick listed...no extras.
The Greenberg's Guide to Lionel Trains has a list of every cataloged prewar set from 1915-1942. Each set # lists it's contents which is where I'm getting all my info. All set numbers ending with the letter W had the corresponding whistle tender and in 1938 the suffix E was used in some, but not all set numbers to indicate a reversing engine in the set. The suffix E was dropped in 1939 on both the engine plates and within the set number.
Up on my soap box now....
With the wealth of collectors literature, I find the minutia important for authenticating originality of individual pieces. Whether each piece was factory packed together in the set in question is hard to prove these days. When boxes are not included, all bets are off. The absolute mania attached to past collecting and its unscrupulous profiteers have all but wiped out any true originality when it comes to authenticating complete sets from the prewar era. Items originally packaged in the set but differing in minutia were purposely swapped with matching items by speculators to prevent potential buyers from questioning authenticity and souring the deal. Add to the fray the factory running changes, material shortages, parts overruns and Luigi's lost weekend, the chances of totally identical sets during an entire year's production is slim. These are the types of prewar sets we have left to conduct CSI's on. It's the main reason I question anything that Lionel didn't actually print themselves. Who's to say the Greenberg's list I'm quoting from is complete or accurate?
Postwar is better documented and far more accurate for sure.
Rant over
Bruce