Theoretically, you could fit incredibly large engines with enough custom work – think big-block Chevy or even some seriously modified diesel engines. However, practically speaking, you'd be facing massive challenges:
* Engine Bay Clearance: Even with extensive firewall modifications, clearance around the engine, steering, and suspension components would severely limit size.
* Transmission and Drivetrain: The transmission and driveshaft would need to be upgraded to handle the torque of a significantly larger engine. This might require a custom driveshaft and possibly even a custom rear end.
* Suspension: The existing suspension would likely be inadequate for the increased weight and power of a much larger engine. Upgrades, or even a complete custom suspension setup, would be necessary.
* Cooling: A larger engine requires a much more robust cooling system. This might necessitate custom radiator work and potentially even a different cooling system altogether.
In short, while you could *theoretically* cram in a monstrous engine, the practical limitations and cost of modifying the chassis and support systems make it a hugely complex and expensive undertaking. Most people aiming for maximum power in a '67 GTO would stick to large-displacement big-block Chevy or Pontiac engines with significant modifications, rather than trying to fit something truly gargantuan.
