* Bore: The 350 typically has a larger bore (diameter of the cylinder) than the 305. This is a fundamental difference in the block itself. While you *could* bore a 305 block out to 350 specs, it's not a guaranteed success and might weaken the block.
* Block Casting: While some castings might be similar, not all 305 blocks are suitable for a 350ci build, and vice versa. Different casting numbers denote different thicknesses and strengths of the block material. Some 305 blocks are simply not robust enough to handle the higher stresses of a larger displacement engine.
* Stroke: While the crankshaft is different (the 350 having a longer stroke), the differences extend beyond just the crank. The connecting rods are also generally different lengths to accommodate the longer stroke.
In short, while they share a common small-block Chevy architecture and some parts might be interchangeable (like some accessories or intake manifolds), the 350 and 305 blocks themselves are distinct and have significant dimensional differences that go beyond just the crank and heads. You can't simply swap parts and expect a reliable, functioning 350.
