the 4.9 6 cly, 289,302, 351c, and 351w share the same bolt pattern. fry & pure are correct in that the flywheels change from early ones with a 28oz weight and later ones use a 50oz weight.(i forget the year...1985 and later i think)
a 351m will not bolt up.
quickest way to tell whick one you have is the distance center to center of the top two bellhousing or block bolt holes. 289-302-351c&w is somthing like 5 1/4" or close to that
351m/400/460/429 are all 7.?something.
360/390/430 bellhousings are almoust round looking, and share the same pattern.
hope that helps