63 was the changeover year from the 261 in 62 to the 230 in 63 and then the 250 in 66 in the big cars. I like the 261 - before a valve stuck, iIcould drive my 2 speed auto parisienne at 80+ mph with lots left. I plan to rebuild it with some performance options and a Saginaw 4 speed for use in an as yet to be determined project.