The displacement of the 289/302 is dependent on the crank, as both 289 and 302 blocks have a stock 4" bore. As you said, a 289 crank is stamped 1M, while a 302 crank is stamped 2M.
My original to the truck, 68 engine is a C8AE casting. 68 was the changeover year to a 302. This block has a 302...