I was very interested in your description of the NHPH and its problems.
My recollection is that the Goucester design had a friction wedge on one spring post (the outer one) on each pedestal. These were much like the bolster wedges on a Barber bogie, where the load carrying springs carried the friction wedges. There was only one, intentionally, to reduce the risk of locking that occurred on the modified Goninan bogies (at least in theory).
The NHPH must have been a lot heavier than the preceding NHRH, the original "Batwing" design. The NHPH had coal sheilds over the end platforms while on the NHRH, the platforms were not long enough to need them. Again, the NHRH were almost all stainless, while the NHPH had a lot of painted steel visible. Of course we since got the Chinese RHHH and NHWH wagons using no stainless steel at all.
What steel was used for the hoppers and lower sides on the NHPH?
Was it mild steel or a high tensile type?
Were the NHQH really the same?
Did Freight Corp ask for the composite construction, and what was their reason for wanting it? (assuming anyone said what it was)!
The recent Bradken wagons NHYH, PHYH, NHEH and PHWH are almost all stainless with only the end subframes in mild steel. All these subframes were made in China, although many of these wagons were built in Braemar or Karribin. These also have a very small centre sill just like the QR QHAH and QHBH and QR NG wagons.
However, the very latest cars, the NHDH have more mild steel (or at least more painted steel) with all the support and bracing for the end slope sheets being painted steel rather than stainless on the NHYH.
I was interested in your comment about the hardness of the stainless in the NHPH. Some of this would be work hardening due to the cutting and bending required, I guess. Budd got around this by using high power spot welding in their passenger cars.