* Original Carb: The 1978 305 Chevy Custom Deluxe likely came with a 2-barrel carburetor from the factory. This was common for fuel efficiency in that era.
* Intake Manifold: This is the crucial factor. A 2-barrel intake manifold will *not* work with a 4-barrel carburetor. You'll need a 4-barrel intake manifold designed for the 305 small-block Chevy. Installing the correct manifold is a significant mechanical task.
* Other Modifications: Switching to a 4-barrel will likely require adjustments to other engine components for optimal performance. This might include things like jetting, camshaft timing, and possibly even exhaust modifications.
* Performance Goals: The 4-barrel will generally deliver more power than a 2-barrel, but this comes at the cost of potentially lower fuel economy. If you're aiming for increased performance, it's a worthwhile upgrade, but if you want to maintain or improve fuel economy, sticking with a properly rebuilt 2-barrel is probably better.
In short: You *can* make it work, but it requires more than just swapping the carburetor. You'll need the correct intake manifold and might need other tuning adjustments. It's a significant undertaking, requiring mechanical knowledge and tools.
