Looks like some one added it on (poorly). You can buy replacement EMPI arms with the roller pedal for $15 dollar . There is a billet version at $25. They were originally used on 1957 VW on back. Springs for the pedal assembly are also available.
Unfortunately that's for LHD. Mine is RHD.
I think having read some more on this I can understand why they used the roller -standard floor pedals can fall back to the floor, and also get in the way when hitting the brake - whereas the wheel has a smaller profile (not in the way of the brake pedal) and rotates when pressed so has a more fluid action than a VW flat pedal.
So I might keep the wheel but fabricate a better arm extension that the squashed bit of wobbly pipe on there at present! (until something better comes along).