You can't just change the water pump, you have to change the front cover as well because not only is the bolt pattern different, the depth of the cover is different as well. You can get a snout extension kit from Hughes to put a fuel pump eccentric on the short snout magnum cam. Now if any of your LA drive accessories bolt to the cylinder heads you will need to address that as well because the bolt bosses are not the same. It's best to just add an electric fuel pump and leave all the magnum accessories in place.