Welcome to the forum. Looks maybe to me like it’s what would be considered a “CX” scratch mark, just with the letters right next to each other. What is the current bore size? What is the date code under the oil filter pad? Can you take a picture showing the deck surface? What size is the small distributor pilot hole down where the distributor sits? Can you take a picture of the passenger side of the block along the oil pan rail? Have you looked down in the water jackets to see if they have “428” cast inside?
