I'd like to say something out loud in the hope that I won't have to do it myself.
To an extent, the style transfer program EBSynth is capable of matching the look and quality of an image when switching from one source to another.
It's not what it's designed for, but it can certainly buy you a second or two when switching sources.
I have also been using it for colorization, as explained at my Youtube channel.
The Conquistador Coffee and Bus Conductor sections on the Python Blu-Rays are included only as extras in lower quality, along with other stuff that's floating around.
If EBSynth is given a sequence of the lower quality shot, and a matching frame of the higher quality version at the same size (the frame where it cuts off, on either side), it can attempt to generate the frames.
It will smear after too much motion, but it will start out well, giving you time to dissolve to the lower quality source if needed, and match the coloring also.
Here's a quick example from "Little Shop of Horrors." I considered this unfinished, as I could have done a lot more with stabilization and cropping and making sure the sources matched. But I've reinstated a deleted line here from various lower quality sources, while retaining the basic look of the shot.