you need to know what PLATFORM they built the Pontiac gto and the chevelle on, that will answer your question , because unfortunately I do not know.
But I telephoned my friend at GM Oshawa and he said the gto 64-65 is built on the tempest platform. Common to Pontiac only.
Starting in 1967 the gto-- chevelle ---buick skylark--olds cutlass were built on the same platform as are other models built on specific platforms
mike