Sorry to hear of the bad news, Amir..it's quite a saga this Selbach of yours. It would have been quicker and easier if I had let you have mine!
I think that Neil is very correct in his diagnosis of the problem and of one way of removing the dent, and I would suggest that there are several methods of easing the dent back into shape.
Not having seen a photo of the damage I don't know how badly misformed the bottom headlug race-housing now is. If the damage is slight it should be possible to remove it by inserting a loose bearing race and exerting some downwards and inwards pressure on it using some form of a press such as a wide pair of vice jaws..or by adapting a head-race alignment tool. This method would use the contour of the loose race to recontour the race-housing of the lug.
If the damage is more acute them I suggest that a little light-handed blacksmithing might be needed. I would probably make up a simple chasing tool, resembling a small cold chisel, probably using a piece of hardwood, or brass, or mild steel. The business end of the tool which might be about 1" or so wide would be filed to the radius of the head-race housing..and to the internal concave curve of the housing.
Judicious use of a hammer to tap the tool into the damaged area, approaching gradually from the side rather than head-on would probably do the trick.
An ideal tool would be a silversmith's bossing mallet, the narrower end of which could be filed into the appropriate radius and used directly on to the frame. The mallets are made usually from boxwood, occasionally lignum vitae, and would be both hard enough and gentle enough at the same time..do you get my drift?.. to tap out the bent-in steel without damaging the frame or stretching the metal. Similarly a silversmith's raising hammer would work well, but would need more care. You must a few silversmiths out in your neck of the woods, Amir
Hope those suggestions might be of some use
Norris Lockley...Settle UK