Many years ago Chip at C4 Labs posted something up on Vintage iirc about replacing the spider on a set of cranks. They had a spider fixed like this, note the fixing "welt" over the spider from the crank arm:
Maybe have a search on Vintage or BMX Society as it is now or maybe just a Google search, it might be something Phil (Sawzall) could help with too in terms of removal and refitting a new one.