8mm: track perforation hole and mask out

How can I track perforation holes, mask and fill with other material?

I scanned many old, long running regular 8mm - not super 8 - films. As cameras at that time produced only unsteady material in low resolution, I had to stabilize it. Stabilization with fusion and tracker to the contents works fine, but now sprocket holes and image boundaries dance around the stable frames a lot.

To reduce the problem, I, of course could zoom in, but I would loose a lot of details.

Another solution would be, to mask out these annoying parts and replace it by an enlarged, blurred picture of the original. Something like what is done to 4:3 material which will be shown in 16:9 format. But here, the mask has to follow the sprocket holes.

As I am relatively new to fusion, I haven't found a solution yet.

I guess you have the same problem solution like how the likes of video stabilization in video camera's work....
a camera uses only a small part of the sensor so you film at a lower chip resolution.
translated to your situation would mean to use a smaller cut out of the image, and blow up this portion, to fit it full to your used aspect ratio, leaving the "wobbely" things (cut) out.
You should translate this to the software you're using, with Davinci Resolve this would be easily done some functions you can "drag" and "click" with the advantage that you can see what you're doing.
this would be the "cut" solution which leaves you with a lower image resolution, but with a full screen,
another option would be to mask the wobbely portion, this will be more complicated, and not full frame active image information, and what i understand you want to fill in.... makes thinks too complicated for me...