Hi pgtr ! We have a lot of guys here with Marx trains & they will be along to answer your questions ! I think you will find some info at this site below. Afriend of mine found a bran new Marx boxcar in the box in the trash once , when he worked at some plant there in Girard , Pa, so I’m sure they made some seperate sale rolling stock. Hope this site has some info for you !
Matal gears, no whistles, in the fifties or sixties.
The 333 is the steamer of choice.
All are tuff little engines.
I have a bunch of Mark and add to them from time to time.
I bought a entire marx layout a few years ago made in the early fifties. I thad the kids manes under it and re-did the table, cleaned the track and swithces.
The 666 engines are nearly bullet proof. To answer your other questions, no Marx did not sell the engine separately, but they are widely available today. Sorry, no whistles. The plastic couplers were on the cheaper sets that came out in the late 50s/early sixties. Marx couplers are a topic to themselves as there was such a variation - hook and slot, dummy plastic knuckle, and the twist couplers. One good thing, it is fairly easy to make idler cars with different couplers on each end or have separate tenders with different couplers. I mounted Lionel trucks on a Marx tender so my 666 can pull Lionel traditional size cars.
Marx put its whistle in the Girard station. I imagine the patents on the Lionel whistling tender hadn’t expired yet, because AF used a similar tactic, putting its whistles in billboards. Not sure if it’s coincidence or not, but the whistle in my Girard station sounds just like the whistle in my PW Lionel tenders.
I’ve heard the reason Marx numbered that loco 666 was because it “smoked like the devil.” Not sure how true that is, but it sounds good.