Any motor swap is a project man, nothing "just pops in." I mean it can be accomplished in a weekend if you keep it totally stock, but then you have a car with a swap that's not really any faster than a stock WRX.

Supra insurance will probably rape you. 300ZX, I dunno...maybe. You can find one in decent shape for about $10-$15k, at least when I've looked for em casually. I think you'd like that the best.