Wasn't the original blue "Grand Prix" car done independently, with Dick merely lending his support to the project? The later project (the yellow XE), was done by Dick, and the development then furthered by Ford IIRC, with their own run of 6 or 7 prototypes... and the project ultimately abandoned. Dick then persevered with the "SVO" XF, as much to gauge public reaction as anything else.
The HDT model worked, simply because Holden wanted it to: Holden dealers stumped up for the cars and the capital, Holden stumped for the parts and a "pay me back later" sort of thing.