Upgrading the Lionel 6-9135 N&W 4 bay covered hopper with opening hatches

The 9135 N&W hopper came in two variations as I recall, which you depict in both the top and bottom pictures.  Light blue with carryover AAR trucks from the postwar period (modified for the new fast-angle wheels & needlepoint bearings) and the more subdued blue that came equipped with the new (at the time) Symington-Wayne trucks that became the standard plastic truck during the entire General Mills era and up until around 1989 in the LTI era.

Neither variations of the 9135 had the plastic truck mounting frames you show in your final picture; they were made of stamped steel.  Plastic mounting frames came later on in the General Mills era; I believe around 1978 or so.  I think the 6-9213 M&StL hopper was one of the first ones, if not the first.

And as I recall the 6-9213 and some other hoppers came with die-cast sprung trucks which were too heavy for those plastic mounting frames and caused them to break.

Bill

You are correct.  I have these similar Lionel hoppers with either stamped metal parts or plastic parts as shown.

The covered hoppers with metal parts do not have any end brake gear.  The plan is to add brake gear to these hoppers in my collection as well.

Attached is another similar Lionel covered hopper with metal parts and plastic trucks.