[silicon212]

If it's a right-hand dipstick block (which all 79-85 blocks are), look on the side of the block near the oil pan rail. A 305 should have "201" on the casting, a 350 should say "207". Aside from this, the only surefure way to tell would be to pull one of the heads and measure the bore. A 305 will be ~3.74 inches and a 350 will be 4.00 inches.