A better way would be to look at the casting number. It's located on the lower right hand side partially hidden by the starter. A Ford 260 casting part number would be C4OE-6015-B or -E (there are earlier castings that start with a C2OE-, or C3OE-). A 289 casting would be C4OE-6015-C or -F, or C5AE-6015-E (again, there earlier, and later castings).
Jim