Are the GM US spec l67 long motors which are available from the US compatible with Holden l67s?

There would be some differences such as; inlet manifolds, supercharger, supercharger elbow, throttle body etc. The sump will need to be changed along with the oil filter mount and/or possibly the timing cover but their prices certainly aren't bad. Please be mindful though that these are still only standard build motors and you'll also need to take freight and import duties into account. The point we are getting at is that it may not cost much more to have an old Australian l67 motor performance built from a reliable daily cruiser to a dedicated race engine. We regularly work together with some of our trusted engine builders which we can recommend for the job.