A Chevy 305 has a 3.74" Bore with a 3.48" Stroke. A Chevy 350 has a 4.00" Bore and a 3.48" Stroke. So technically its just a smaller bore. The 305 heads are 53cc chambers and can be put on a 350 to increase compression, but at the minor expense of flow. Plus the 305 heads crack easily. The 350...