The 'springy thing below the end cab window' is a 'subway gate,' type of thing, to keep people from trying to jump onto, or off of a moving train. They became standard on the NJT Comet cars, with either the Comet III's or IV's. They function like they do on subway cars-keeping people from jumping onto, or off of a moving train. They transfer none of the physical load between the cars. Back in the 1990s, NJT had several instances where (maybe drunk or high) people: climbed to the top of the cars, when Midtown Direct service started, while running underneath the Hudson River, and got electrocuted by the catenary, tried to either jump on, or off a train pulling into/out of a station, and got run over, because they either a)missed their train, or b) missed their station. The 'gates' were to prevent this sort of thing from happening as frequently. Additionally, they cut back on the availability of liquor being sold at the departing terminals(NY Penn, and Hoboken). Hate to tell you the number of times I'd be taking the train home from college, only to have the odd 'empty' beer can rolling around on the floor of the car, the whole way home...There were actually Comet I's that had a small bar area that served drinks, when first delivered. One or two of the side windows were either blacked or blanked out. I think Conrail ended the staffing of the bar cars, when they took over, however the bars weren't actually removed from the cars, until NJT came along in 1983, as I recall. I commuted to college in Newark, on the Morristown line in the 80-82, and remember being in a bar car, several times. Very useful during fan trips, also.
The Walther's Comet car is closest to a Comet II car-no middle doors, no 'subway gates,' as originally equipped. Also, doors did not drop below the traps, like on the Commet I's that only the EL had, originally.
Black thing around the door is a 'diaphram.' American Models Limited, or something like that might make an appropriate one.
Another difference is that I don't believe on the Comet III's there are any steps below the engineer's compartment, on the cab cars. Might be a 'holding tank' below the engineer's compartment in your photo. Something to hold sand wouldn't make any sense, as the car is 'unpowered.'
Hope this helps.
. The Comet 1s were somewhat different from the rest of the Comet fleet, as I recall.
