Will a 1967 Pontiac 400 engine block bolt in 1968 gto?

Yes, a 1967 Pontiac 400 engine block will generally bolt into a 1968 GTO. The engine block itself is largely unchanged between those years. However, you'll need to verify that all the accessories (intake manifold, carburetor, distributor, etc.) are compatible and that you have the correct motor mounts. There might be minor differences in details, but the fundamental bolt pattern remains the same.