ok the bore for the cylinder are the same for 351 and 302 right? but the rod length is different right? so i use forged pistons from a 302 and change the rod it should fit in a 351 right?

 

there was a stroker crankshaft i was looking at made by eagle that calls for 302 pistons. so as long as you figured out what the correct rod length would be, it would work.

 

i believe both have a 4 inch bore, but usually with a 351 u need dish top pistons. I am not positive about this, so if im wrong someone correct me. I do know that the rods are different, so in my mind you should be able to do this as long as your compression isnt too high.

 

they are different pistons

 

The deck heights are different between 302's and 351's.
Bore is 4" on both. the 302 has a 3" stroke and a 351 has a 3.5" stroke.
Bore spacing is the same, that is why 351W and 351C heads fit on 302 blocks.
Changing rod length will move the piston up or down in the bore relative to crank position. The piston will still move the same amount ie 3.5" in a 351.
The main difference between 302 and 351 pistons is the distance from the top of the piston to the pin. 351 distance is shorter due to longer stroke and longer rods.
If you wanted longer rods in a 302 you could use a 351 piston and a slightly longer rod, if one is available in that length.
Swapping rods does absolutely nothing as far as displacement. you will not get a bigger engine from it. You must either change the stroke or the bore to change displacement.
Deck height (the distance between the crank centerline and top of the block) is the main determining factor in rod length. Then stroke and how short you can make the piston and keep it stable in the bore.

Putting 302 pistons in a 351 would require a much shorter rod as the pin is lower. It is cheaper to replace pistons than it is to change rods.

 

To use a 302 pistons you can run a stock length 351w rod with a 3.85 stroke crank. Ford Racings 392 motor is this way. They don't do well in high rpm applications.Or you can run a stock stroke crank and a 6.125 rod and it will drop your compression some. You just have to know what compression ratio you want.

 

what does this do to your total stroke length?