If you're starting from scratch, and honestly don't believe 500-550fwhp will cut it (and that's power enough to run well into the 10's BTW), then I wouldn't bother pissing around with a stock 302 block at all. While I'm at it, I believe for most, even a Dart block is a waste of money unless you plan on making 1,000hp+ and are dead set on sticking with 302 based components.
For the money, you can't beat a good 351W build. The block is twice as strong as any production 302 and can be built for half the cost of a Dart. Not to mention have tones of room for displacement growth. You can stroke and poke a 351W to around 400ci for around $1,000. I spent nearly that much on my 331ci rotating assembly.
In any case, once you reach that 500-550hp threshold, things really start to get expensive.
Honestly, if that's all you're after then you don't need an aftermarket block, or a 351W....or rotating assembly for that matter. An Explore long block, mild cam, some basic bolt ons and a used S-trim stuffing 8-10 psi down it's throat Will easily meet, or exceed those power levels.
No need to make things difficult. Turbo kits are trendy, but they are a pain in the ass and over rated for your average consumer in my opinion. Bolt on a tried and true blower combination and don't look back.