The US motor mounts are not available. The mounts for the US Manta are different than the versions on the European versions.
The European Manta mounts are the version similar to the '71-73 US cars. The '74-75 engine cross members have a small bracket welded on to accept the bolts for the that specific US mount. The original '71-73 mounting hole is still present on the cross member beneath the bracket added for the '74-75 mount. The change in style was designed to keep the motor from leaping into the radiator if the mount broke, or so the speculation has it.