The 0-6-0 tank engine looks like HO. I seem to recall Marx also made a nice diecast HO Hudson that had similar turned drivers.
The signal is an O-gauge item. I have one, but need to find a couple of bulbs for it.
Marx made a lot of ingenious trains and accessories, but never got much respect, probably because the line was priced at the bottom of the food-chain. No matter, Marx locos are about as bullet-proof as they get. Never had one that wouldn't run with just the slightest care.
My brothers and I each got a Marx clockwork set for Christmas one year. I can remember us taking the track from all three sets to make a mega-loop to run the trains on. The locomotives were stamped-steel construction, as were the 6-inch freight cars (similar to the ones sold with the electric sets). Had a lot of fun with that stuff, but we needed more track!