* Bore: The 305 has a smaller bore (4.00 inches) than the 350 (4.00 inches). While this looks identical, the *stroke* is what differs.
* Stroke: The 305 has a shorter stroke (3.00 inches) than the 350 (3.48 inches). This is harder to measure without taking the engine apart.
Therefore, you need to measure the bore and stroke directly to be absolutely certain. Or, if you have the engine's casting number, you can look it up in a parts manual or online database to determine the displacement. The casting number is typically stamped on the block itself.
Other visual clues *might* suggest a difference, but are not reliable:
* Intake Manifold: The intake manifold will be different, but it's easily swapped, so this is not a definitive indicator.
* Valve Covers: Similarly, valve covers can be changed.
* Exhaust Manifolds: While the exhaust manifolds *may* be different, this is not reliable.
In short: Measure the bore and stroke for certainty. Look up the casting number for a probable identification.
