The deal is you should loosen that bolt before disassembling the whole thing. That way the spring applies pressure to the damper to hold it still, then hit it wiith and air impact or the like. Then disassemble the rest of the tube and take that bolt the rest of the way out.
On the early 750s hondas parts book doesn't even acknowledge the existence of that bolt and damper. They are never to come out. I have found taking one out that there can be a lot of crud to clean up.
If the fork is already disassembled, many will shove a broomstick or fat dowel into the lower leg to hold the damper still. Put the piece of broomstick on the floor, insert the lower leg over it, press down, then hit that bolt with an impact, air,hammer or otherwise.
At the stage your at drilling the head off is likely your only hope. Then the damper will fall out with what's left of the bolt still in it.