Now that I've been here so long you've got me thinking of your problem. What part/section of your trunk weather strip channel is rotted out? Down near the tail lights, up by the hinges, where? What I'm getting at is do you need the whole channel 360 degrees or just sections. If you need the whole thing you'll probably be better off to find a 66 donor car (what about 67?) if all you need is sections you might get lucky and get the right profile of material from something else in the 66 era. Maybe an Impala? My buddy is parting a 66 Impala right now. No matter what, you've got welding in your future