Hi JB - What I "know" for sure is - We will be offering 7600 series flarcar kits in 36' 38' and 40' (actually originally OLC cars that ended up on the SVRY). The cars had T section Bets, arch bars and Vulcan trucks - although this must be referenced to the different stated capacities in the car roster you graciously donated to me.
The drawing in Ferret's RS&P of a 7600 series flat is apparently from PAACar - the original maker of at least the 36 and 38 foot (and probably the 40's as well).
The one picture youse guys put on this list of the 7600 flat on it's side is wonderful but i think it's of a OLC 40 footer. (6 truss rods?)
Because there are no kits for more modern 36-40 foot flatcars on the market these may appeal to non SVRY modelres and maybe not. At least when this deceptivly complicated kit is done then everything else put on top of the flats (block car, logging flats etc) will be abreeze.
Lon