Neville,
I used Evergreen Plastic stock to make new frames for my weaver express cars. I found that lining up the various holes was much easier when using plastic.
Another word of caution,- be careful when you take the cars apart. The center sill for the car can be easily be broken when you take the car apart.
Remove the four small screws holding the center sill on the frame before you attempt to remove the car body from the warped frame.
I would go ahead and take your cars apart now.
I still do not know why Weave will not step up and do the right thing for their customers.
Richard