Ordinarily, the fuselage in a plane of this size is large enough that you can simply reach into the nose and run bolts through the fire wall. If that isn't possible, you can use bolts and blind nuts. Drill your holes for the blind nuts into the firewall. Then run a piece of music wire through the holes sliding the blind nut on from the back side of the firewall. Then pull the nuts up to it as tightly as you can. Use bolts to tighten the nuts down so they dig into the back of the firewall.

By the way, I would love to see some pictures of your Spacewalker II. I have one that I haven't gotten around to building yet.

Brian