Phil correct me if I'm wrong.
Ok here ya go. Buick powered can be anything. Olds, Pontiac, GMC, Saturn etc. must be the power plant they came with or Buick powered. We know anything late model is corporate GM like my Rainier.
Im going to race my tow vehicle it is a '05 Buick with a 5.3 V8 but it came that way from the factory. Don't worry it's slow.
I was kidding with the Ford powered Bird... I know if it showed up it would run for the Fords. It does not qualify to run for the Buick side.
Does that muddy the water some more?