Michael, all Americans like chewing gum, so chew the gum while getting things ready. You will need a length of dowel, and your coathanger wire. Ready ? Put a dob of chewing gum on the end of the dowel, now press the nut into the gum, that holds the nut ok . Now with the wire put it through the firewall hole and locate the nut on the dowel, pull the wire back at the same time as you push the dowel in, till the nut reaches the firewall. Hold pressure on the dowel to keep nut in plave , and carefully hit the other end of the dowel to seat the nut in place. Finish off by putting washers on the bolt , screw into the nut , and do up tight , to fully seat the nut in place, the refit the motor mount. No hassels and all is well. Good luck wit hthe rest of your repaird, and good flying my friend.
Bill