What is the difference between a Chevy 305 and a Chevy 350?

The bore and piston size are the only real difference between the two.
The 350 has a bigger bore and piston and so puts out more horsepower, the
305 = 3.75" bore and the 350 = 4" bore. Both have the same stroke.

Also the starters are different because of the smaller flywheel but other wise the external parts are interchangeable.