I don't know, man. It seems like you've narrowed it to a 302 with rods or a stroked dart block. The difference is time and money, and that's it. You have to decide. If you want to spend the time and money on it, go with the dart. If you want more flexibility, to get it back on the road, and to leave yourself more flexible in the future, and to have the option of making that power indefinitely at a mere fraction of the cost, then go with the stocker. It's not 'overbuilt' at 450rwhp, but it's just about right. That's my vote, but if your mind it made up on "overbuilt," then you have the answer. The stocker is not... it 'might' fail, but fixing the failure is cheap and easy.
Regarding pulley size, aren't we talking about a positive displacement blower? So, same pulley size = lower boost and same amount of air, which = more hp, because it comes in at a lower temperature with denser air. I don't see the issue, and you're talking about a 347, anyways. So a 351 is not ruled out by the displacement argument.