Nevermind, I found out those by trial and error. The turret mounts to mount1.
But now I have a dungheap of problems with the model, lighting and other stuff.
Recalculate normals messed up the lighting even more, and when I shoot the turret, the player is moved to the centre of the turret from the original mount position.
EDIT: Also, the collision has a different dungheap of problems. The "wheels" do not seem to function at all, and the whole thing sinks into the ground for a few seconds, then springs back up, sinks back down and repeats.
EDIT AGAIN: What node do I give to the barrel so that the shell fires from there?