Complex sentence: They featured modifications for the New Zealand market including the continued use of the Rambler marque however the NZ Matador was considerably more "American" than it's neigbouring Australian model, whereupon Australian rules required more local content for tariff concessions.
Split into simpler sentences: They featured modifications for the New Zealand market including the continued use of the Rambler marque. The New Zealand Matador was considerably more "American" than the Australian model, since Australian rules required more local content for tariff concessions.