Harry,
If you google in Holden straight six there is more information about these motors than I could tell you. My own interest is in the grey motors which were a scaled down version of the GMC engine. Originally producing 60 hp they were made to produce up to 200 hp and were probably one of the most modified engines of all time although probably unknown outside of Australia.I personally have 21 different types of intakes using all sorts of carbs and there are lots more that I dont have.There were at least 4 different aftermarket heads including twin ohc, a twelve port crossflow and a rotary valve head that would allow the engine to rev to 9000rpm.Hope this may have been of some interest.
