Here is a Marx 528 set (I don't know what the difference is with a 526 set) and a Gilbert American Flyer NYC Hudson set:
Fred
Fred, that #528 Marx Mechanical set is interesting. The only difference I can spot between your #528 set and my #526 set is that you locomotive has the cover over the bottom of the motor. For most of the years of production of the 401 mechanical, the motor was open on the bottom. I know for a fact that the #526 set sold up to 1972 didn't have the cover on the bottom of the locomotive. The later #530 sets (with 4 wheel plastic cars and plastic track) include a 401 locomotive that has the motor cover, but is made of a gray colored plastic instead of the black plastic typically seen in the earlier 401's.
I have quite a few 401's - I believe I have all the variations - and I do have one that appears to be completely original with a black plastic body and motor cover. I've always left it as-is, and now I'm glad that I did. I'll be on the lookout for a #528 set for my collection - thanks for sharing the video.
Here is a #530 set from my collection, circa 1975ish. Note that the cover shows the set with a 401, tender, yellow SCL gondola and red Santa Fe caboose - that is how most of them came. However, a few have surfaced like this one that include the green Erie flatcar instead. Marx has a lot of fun variations to collect!