351W VS 302

There is no replacement for displacement, my friend. The top end you have now won't feed a poked 351 very well, but you'll see performance gains from the increase in displacement alone. Keep in mind you'll need a 351 lower intake, because the 302 and 351 have different deck heights, thus different size lowers. Also, the cylinder head bolts on 351Ws are fatter, so you'll need to drill out the holes on 302 heads.

Aside from parts fitment, the 351 is taller, so using a cowl hood or "drop mounts" are necessary.

you should see some gains from a new 351, but i would think that you would see just as much for less money with some new heads. the swap to a 351 would cost you some money up front, but give you more to build on later (more potential) but some nice alum heads would cost you about the same and give you more power now. just my $0.02.

unless you can find a deal on a block, assembly, headers, pan and lower intake (and you'll need heads with bigger bolt holes anyways), then I would say just find a nice set of RPM heads or something.