Can a modern car engine fit inside an old car? If it does, can it work?
Fitting the engine in won’t be a problem. As you noted, older cars are larger with plenty of space in the engine bay. The problem you’ll have is making the newer engine work in the older car. Newer cars have multiple sensors, computers, and subsystems for traction and stability controls, transmission controls, anti-lock braking, and in some Cadillacs, even electronic controls for the shock absorbers.The bummer part is that if you remove some or all of these subsystems, the engine management system may not function properly to run the engine normally.A better option for your purpose would be to buy what is called a “crate motor”, which is a motor specifically designed to be used in multiple types of vehicles. GM makes crate motors, and sells them through Chevrolet dealerships. Here’s one that might interest you:LSA Crate Engine - Race EngineThe LSA V8 is the same motor used in the Cadillac CTS-V, and if you add the “connect and cruise” option, it would be relatively easy to drop this motor into an older car.