Definitely oxy/acetylene to heat rivets cherry red, on the parts to be assembled. Use two people - one to work the torch, one to mushroom the rivet. Do it in two steps instead of all at once for a more controlled process.
TD
I have been stung more than once by bees and wasps. Worst time was when I was using a cutting torch and the wasps came out from the other side of the panel. I always keep a can of bee spray handy now.
TD