I may have missed the reference, and as a three-rail non-scale guy, please excuse my intrusion, but did you consider the Elliot Welz models in your search for ends? Would they be of any use to you in your project? I have several sets of them and would be willing to lend them for research or copying, etc.
Thanks, Arthur, no intrusion at all. I am looking at the Williams cars and their parts because that's what the Benson models were based on, and everything will fit. I don't have any of the Welz models or parts for comparison, but I always liked their cab ends more, compared to the Williams models. The Williams 'B' Ends that come with these Amfleet kits are actually Metroliner ends, and similar in detail and appearance to the Bachmann HO ends, oddly enough.
I got two coach kits and one dinette kit, and I'm thinking of using one coach and the dinette for this project. A 2-car MU set would result: one coach and one food service car. I'd have the extra coach in reserve in case I ever decided to build a third car.
Another idea I had for trucks was to use the GSI trucks from the Atlas Horizon cars (the Amtrak versions). They are nearly identical to the Metroliner trucks. I'll make new underbody from CAD/3D printing, and build a power truck. I can see myself building a Stemman pantograph for the coach, and I could probably use the Faively pan from a Williams or Welz unit on the food service car.
This Metroliner project is mostly just for me. I have no intention of producing O scale kits myself at this time. I'd just like to get a couple of cars for operation now and then. I don't do enough projects for pleasure these days.