Why? I hope not because you have a used one lying around...a cam is something that isn't going to live long in a re-use situation, if you believe traditional advice.
The lift and duration will vary, you can buy a wide range of them for the 351, just like you can for the 302...so there's no benefit in one over the other.
The firing order will be different, and that's the only reason I can think of to change the cams. The 289/302 firing order puts a little extra stress on the front main bearing that the 351 will relieve a little, but unless you're really talking about a lot of power or hard driving it's more precautionary than anything else.