Quick answer: Start off with a DE-T. They're plentiful, the engine was designed for boost, and converting a [rare] RB25 is going to be a colossal PITA. The heads and block are indeed different.
I have had an RB in a '72 Z for 12 years, so you're on the right path. NEO or not isn't crucial, I prefer the earlier engines (if you can find one). Typically, they'll need re-sealing and a good inspection, but they're pretty bulletproof. Any straight-6 is an inherently well-balanced engine to begin with, so either FW should be fine (no real reason not to use the stock one).
You shouldn't need to worry about AWD conversion - That was the RB26DETT.
Make sure you get as much of the original stuff for the engine as you can - ECU, harness, MAF, anything you can get. Sure, you can source stuff, but a bone-stock proper-running RB in a 240Z is a recipe for frequent tire replacement and loads of fun.