Check me on this but I believe the 351 heads are taller., req. a diff. intake.
But then., I didn't know 351 heads would fit/work on a 302....
------UPDATE..!------- :-B
It wasn't long ago that the only choice for cylinder heads was the factory offerings. In the old days, your choices for topping a 5.0L or early 302 basically consisted of stock (E7TE) 5.0L casting, early 289 HiPo heads or the cream-of-the-crop 351 Windsor heads. Actually, none of these offered much performance, at least not compared to anything currently available from the after market. Early Mustang owners should thank their lucky stars that the late-model 5.0Ls became so popular, as performance parts abound for Windsor-based Fords, including cylinder heads.
Read more:
http://www.popularhotrodding.com/enginemasters/articles/ford/0611em_ford_302_engine_build_up/viewall.html#ixzz1oCo7grTy