300 swap
I've not done the 300 swap before but I have put in 2 Turbo Buick's into 82-92 Camaro body styles with great results.
Food for thought: I bought a 89 Nissan Maxima for a winter beater last year. IT has (now) 205,000mi on it and has been boosted for the last 20,000 mi using all GN (theorys) and some GN parts. THe Maxima has the same base Engine block that is in your 300ZX right now. I'm running a TA49 Turbo from John Craig, Made my own pipes to feed the turbo, Down pipe ect. 370CC injectors, Live Edit which I can change fuel/timing tables (Free on internet) 225lr/hr fuel pump and a adjustable FPR.
I'm running 11psi and going 109.7mph in the 1/4mi. I just got tires that will hook and proably nuke my tranny but it'll be fun.
I drive this car every day gets 24mpg in town and 28 on the highway.
I hate the way they did the twin turbo setup in the 300z. IT's fricking impossible to work on. My Maxima has more room to work on it now than it did from the factory.
Putting the 3.8 Buick in will be a good choice too but keep in mind that the 300z engine is one tough and long lasting engine too that can make some serious power. If you converted to a single turbo and a different manifold on the base engine you've already got it'd make some killer power.
What I Did with my Maxima is prove that GN theory works just about everywhere!
~Scott