I once found the perfect engine for a swap in my 240Z, but I procrastinated until it was gone, and I'll likely never find another one for sale at anything near a reasonable price.
It was a 4.9L DOHC Maserati V8 with factory Weber carbs. Now I know what you're thinking: Thats just madness. why not something more common like a LSx motor or a 5L ford? well those motors are just BORING. Nobody wants to see another boring 240Z with an LS motor in it.. thats just too mainstream..
Also owning a Datsun with an engine that usually is found in rare cars that sell for upwards to $100,000 would have been quite satisfying.
Also OP, why not an RB motor in a 240Z?.. 2JZ is blasphemy to Nissan enthusiasts.