I do not have any dent removal experience with .410 bore barrels, but have removed dents in 20 ga. barrels. I can't say that was any more difficult than raising a similar dent in a 12 gauge barrel. Considering that your dent is about 8" from the muzzle, I don't imagine the wall thickness there would be so thick as to make dent removal all that difficult.
Some years back, I built a hydraulic dent raising tool and used 1/2" EMT conduit to test it out. The wall thickness of the galvanized steel EMT was .042". I could make some pretty healthy dents in it, and then easily raise them with the hydraulic pressure of the anvil alone. I know jacking a dent up with hydraulic pressure is NOT the proper way to use a hydraulic dent raising tool, but I wanted to see what it was capable of. I was able to easily produce over 3000 psi of pressure. It was evident that a hydraulic dent raising tool used this way could easily turn a dent into a bulge, even with steel tubing thicker than the average forward portion of a shotgun barrel.
So in short, I wouldn't over-think it or worry that it can't be done. It doesn't take a whole lot of force to dent a shotgun barrel, and it doesn't take a whole lot of force to remove that dent either.