I do not think you can put the heads from a 351 onto the 302. The exhaust manifolds may be a little defferent. And the intake ports, also, may be a little defferent. I'm assuming that you may have the fuel injection. One thing you might want do to get better perfor-mance, is to order the upper & lower intake manifold and throttle body from edelbrock. That will definately help with the performance. Also, mabe a set of headers will help.
I currently have a 90' EB Bronco with the 351W(5.8L). Recently just rebuilt the engine. Still waiting for a few parts. I used to have an 89' bronco with the 302(5.0L)engine. Between the two engines the 351W is the way to go. But it's a gas hog.
Hope the helps
Kimball