I'm having a bit of trouble imagining what you had done with the bolt and welded nuts....

What pedals are they? Seems to me there are some pedals that come with a wider stance, but spacing out most pedals by 20mm doesn't sound good to me. You can take the crank to a bicycle mechanic and he may be able to repair it with a helicoil insert (and ask his advice on options for your pedal).