I did a quick look, but didn't learn what alloy a crankset usually comes from. I believe there is a particular filler metal to use if you're not sure of the base alloy- someone will come back with that info, I'm sure.
In the mean time: do you already have the taps required for this? It may be a specialized deal specific to the cycling industry. BTW The left-side pedal has reverse threads to prevent the pedal from un-threading itself while riding. I saw the proper taps from Park Tool for $35. And looking at how worn the teeth are on those chainrings (the tops start out life as square), I looked up replacement cranksets at Nashbar.com and they start at $30. If the threads are too badly FUBARred to use and the bike just isn't worth the time and effort, you might consider just welding the spindle into place (if the metals allow).
What's the make/model for your bicycle?