Step 1: Materials
For the support legs I used a normal galvanised steel plumbing pipe that fits nicely into the holes that were already in the drum (some sort of connecting holes that connect the drum to the motor shaft...)
Step 2: Cut legs
Step 3: Add legs to drum
Step 4: Finito!
As a bonus: due to all those holes in the side of the drum and the general geometry if the thing, the airflow through it is fantastic. This makes it very easy to light the fire in it.
Step 5: Afterburn
As a bonus I uploaded a video of the firepit in action. Nice! :D