Gas engine stand off mounts??
Use 1.5" dowel rod from the hardware store. Cut 4 pieces the length you need and then drill the appropriate size hole down the middle for the bolts. You can either glue tham to the firewall or not. Use a fender washer and a lock nut on the back side of the firewall. I stopped using blind "T" nuts on gassers. Too many have failed.
Bryan