Nothing weird about it, it's standard A series head drilled for air injection. To the best of my knowledge they were used here in the U.S. and Japan and anywhere else that required emission controls. Like lamb said, for use with an air pump (smog pump). The reasoning was/ is that if one injects fresh air into the exhaust stream, it will cause all the unburned fuel to burn, reducing emissions. As far as performance, it's about the same as an H72 head, possibly slightly worse. If you are going to use it without an air pump, make sure that you plug the hole in the front of the head by the thermostat so as not to have an exhaust leak.