Thanks for all the comments and insights. I can suggest at least 6 reasons why the Vauxhall/Opel cars were not used as a base for the LH Torana. 1)Program and release schedules were out of sync. 2)Australian local content regulations (up to 95%) meant car companies here were forced to use as many carry over parts as possible to save money. The LH has HQ components under the sheet metal. 3)Cost of re-engineering European cars to meet Australian local conditions and roads. Recall that Holden spent $110 million just to ensure the Vauxuall/Opel V-car (VB Commodore) sedan did not fall apart when driven on dirt roads. That cost was a big part of a slide into financial problems for Holden. 4)GM’s division's senior executives were not financially bonused to share car development. So why bother? 5)One of GM’s strengths was its ability to have cars developed for specific countries/regions to suit local preferences: Australia’s Own Car. But that strength became a liability in the 1970s when “world cars” and global safety regulations began to gain a foothold and the cost of developing a new model rose exponentially. 6)GM styling had already tried to convince Vauxhall and Opel to join with Holden to develop a range of cars, back in 1963. But Vauxhall and Opel were not interested. Opel feared losing their styling and engineering independence. Leo Pruneau, who designed the FD/FE Victors and LH Torana, was the chief of design for this project. David Booker at Vauxpedia and I wrote a story about this for Retroautos and Vauxpedia a few years ago. Here’s the link: https://www.shannons.com.au/club/news/retroautos/retroautos-march-gms-secret-1963-plan-to-interchange-vauxhall-opel-and-holdenmo/