this may be a dumb question but will the aftermarket headers from my 302 fit a 351?

 

They SHOULD. The block is the same, it is the heads and the pistons that are different between the 302 and 351.

 

Sorry, that's not correct. The block is very different, but the heads are identical except for the head bolt size.. which you can't see from the outside. Headers and exhaust manifolds are interchangable between motors.

 

They'll bolt up to the heads, but how they clear everything else in the chassis depends on the particular set of headers. The 351w has a taller deck height, and thus, is both taller and wider. Your headers will be further up (toward the hood), and out (toward the fender). Not a lot, but enough to potentially make a difference.