I finally designed, received and painted an Ursus claw for my proteus pattern warhounds. I tried to take inspiration from my previous research. This is a non-symetrical design, but a simple mirror on the STL would do the trick for a right arm version. The chain was a bit tricky, but the result is not so bad (considering my painting).

I have designed a version that should work with the Mars pattern warhound kit. I have NOT test-printed it, you can see it below, compared to the proteus patern.

And finally, I have printed an arm that allows to mount the inferno cannon on the proteus pattern warhounds (or any other horizontal weapon).