chris, i have a 70 lemans w/ a 2001 zz4 chevy motor in it.
the previous owner had the wrong frame mounts and motor mounts in it.
the motor was sitting all wrong.
i got a set of 70 chevelle frame mounts off ebay for $10.00. they bolted right in.
then i got new, correct sbc mounts from the local parts store and all is good, now.
i would expect you could do similar for your car.
65 cutlass frame mounts and motor mounts for your 455.
maybe this site can help you locate your parts.
http://www.oldspower.com/vb/
david