Well, that's one way to get a freewheel off, ha!

Now that you're this far, I'ld definately buy the track cog. As much as I enjoyed seeing your welding handiwork, you're best bet is the track cog route, not as unique, but a whole lot safer, even if you loctite/bottom-bracket-lock-ring it to your existing hub, plus you get to learn to redish your wheel to get the right chain line. TOns of setups like this riding SAFELY out in the wild.