You'll also have to get a new fan clutch. As mentioned earlier, the pilot bore is 5/8 inch for the 460 (right) and it's too risky to ream out the 351M/400's 1/2-inch bore to fit. A spinning fan shearing off a running engine will take out an amazing amount of underhood items and ruin your day. And what if the hood happens to be open with someone standing in line? Bad mojo, baby, yeah. The original fan will bolt right up to the new clutch.