Here's why it's risky:
* Gear Reduction: The 350 (being a larger displacement engine) might require a different gear ratio in the starter to crank effectively. A starter designed for a 350 could struggle to turn the smaller 305, or it could spin too quickly, causing damage. Conversely, it might not have enough torque to turn the 350.
* Motor Power: The 350 starter motor may require more power than the 305's electrical system can supply. This could lead to slow cranking or even damage to the electrical system.
In short: While it *might* work, it's not recommended. It's best to use a starter specifically designed for the 305 engine to avoid potential problems. Checking the starter part numbers for both engines is the best way to ensure compatibility.