I currently have a 306 block with the DSS forged pistons and the Holy II complete kit. I'm getting 340hp right now. I plan on going with a pro turbo kit or a procharger P-1sc kit this summer and making around 450hp.
i like the idea of running the turbo on your 302 for a while, while you build up a new long block. That seems like the best route to go. It may take longer in the end than doing it all at once, but you'll have more fun doing it.