Rick.. i am sad to say.. that was the case until this year! They are new 'cars of the future" format. Hence the inclusion of the Mercs and Nissans this year. They now all have the same chassis, box and diff.. but have the factory body panels and they run their own companies engines. I guess they have a far closer resemblance to street cars than NASCAR.. but it is now a silhouette formula to some extent.
As for FORD.. well they have just announced on Friday that as of 2016 they will stop manufacture of cars in Australia.. so no more Aussie designed and built Falcons..