Make a couple of access holes in the firewall with a 1 inch hole saw, in line with the bolts. Then make round patches for the holes from 16 gauge sheet metal and attach them with a couple of self tapping screws, or use rubber plugs. Some sort of sheet metal butcher has already been there with a pop rivet tool, so a couple more holes won't hurt.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!