How to remove prop from MicroCat pedal drive

[tinhorn]

So I picked up this sweet secondhand, pedal-powered, inflatable pontoon boat last summer and had an absolute blast with it. I'd like to remove the plastic prop and am not sure how it attaches. I figured it might simply be riding on a splined shaft since there were two setscrews in it, but my efforts to tap it off didn't seem to budge it. I stopped when I put a chip in the rear edge.

It appears that opposite the prop there are two holes in the cap. I suspect this cap might be threaded, and if so I can make a tool for unscrewing it.

What do you guys think?