Yes the Buick and Pontiac Big Blocks were the new thin wall designs with advanced casting technics compare them to Chev they are noticeably lighter and more compact. In fact fit the Pontiac in say a HQ and people think its a 350 till they look closer.
There is a heavy hitter GS in Perth engine build was in Perth Street car magazine about 5 years ago made 850hp from memory . It goes to Kwinana now and again its not tubbed just treaded drag tyres does low 11's can go quicker but owner refuses to put in cage. Cant blame him it is a real GS spoke to him about 3 years ago at the drags. Genuine motor in storage.
If I find the article on the Perth Street Car I will let you know engine build was a feature. And Listed by brand what parts used and it was 800hp engine.