Sounds like a great job with the engine. Was it a Mopar engine builder that did the rebuild?
Great idea making it more user friendly for your dad. One safety upgrade many do is replacing the factory one-pot brake master cylinder with a dual master cylinder. The dual master cylinder allows you to keep brakes to one end of the car (front or back) if the other develops a leak.
I have an extension on my kickdown linkage but it was already there when I got it. Its an extension that screws into the rod, then the end in your pic screws into it. Hopefully someone will know where to find them.