What I managed to figure out:
Most of the files are probably Gerber-274-D.
The .DRL is an Excellon-alike-file or an Excellon file with a corrupted header.
Usually you will find the drill table in the header of this file but the header doesn't make any sense (just random characters), this means I can extract the coordinates of all drills but I cannot extract the sizes.
There are only 15 drill sizes though so it would be in the realm of possible to restore the drill size with a lot of time and research. (I would need the schematics so I can search the correct drill sizes of the connectors etc).
Then there is the most important file, the .gwk file. This is a GraphiCode project file and it includes some necessary information like the aperture list.
You can request a free trial of GraphiCode on their website (
http://www.graphicode.com/ ).
It is very likely that this file also includes a drill table or at least it 'should' do so but I cannot find anything usable.
If you want to reproduce everything by yourself you have to download Graphicode and Open the gwk file with it (all other layers must be in the same dir). To include the drill layer you will have to delete the first line (the corrupted header up until the '%') then you can import it into Graphicode.
The drill layer also needs to be rotated.
So what you need now is a way to either extract the drill table either from the .DRL file or the .gwk file or you have to search for the drill table somewhere else.
I assume you have an assembly pdf, a BOM and maybe a schematic. With this information it would be possible to recreate the drill table.
Sometimes PCB designer also include a Drill guide output with the drill table (pdf or a picture or something like that). If you have something like that it would be really easy to recreate the drill table.
I have included Gerber-274-X output of all layers with standard Altium layer names (except the inner layers which are called gl2 and gl3; I do not know if this order is correct).