Try smacking the easy out with a punch, you might be able to shatter it and draw it out.
If not, you can heat it up red hot, let it cool slowly, and it should be soft enough to drill it out.
If you get the easy out drilled out keep going up in drill size. Don't go over 5/16" because that is the base drill size before tapping for a 3/8" coarse thread hole for the mount. Then try an easy out but use the straight type not the screw shaped type, and don't over do it.
Some heat and wax might help before trying the easy out.
If you have to, drill out the old bolt and re tap or if the hole is too damaged go up one size to 7/16" and drill out the motor mount hole to match.
Be very careful not to go any deeper on the hole, there is a water jacket very close.
Check my web page for First Gen Camaro suspension info:
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Can Am Vintage Racer