Motor swap with less headache.
 

Bought a Lucky7Racing swap kit for my Miata to drop a 13b into it, now I need a motor. I know a REW won't fit with the factory turbos and I would need to go single or I can do a S4 or S5. I know the 13b's have electrical issues from the heat cycles being so intense and I plan to just go with a stand-alone ecu like the Apexi Power FC or the AEM unit. Cost isn't too much of a big deal but preventing headaches in the future is. Which motor will the be the easiest to work with and will doing all aftermarket gauges and making my own harness for that be easier than trying to get a factory cluster to work? I'll be using it to race the local tracks and autocross and occasionally drive to work for the hell of it.

The kit is designed for the 2nd gen rx7, so just get a S4/s5 13bT.

if you are planning for big power then you want the reinforced s5 rear iron. if you want to live at under 350hp then the thin iron might be fine.

the benefits of the Power FC is that it is plug n play for a factory harness.

if your wanting to build your own harness then you can go with whatever your tuner is familiar with, but these would be my top 4 standalone for under $1500:
Fuel Tech
Megasquirt
Adaptronic
Haltech

I plan on living way below 350hp. My plan was 225-250 so it sounds like the s4 will work fine. I have been doing some research and it looks like the S4 is easier and simpler to work with. I'd like to use a Power FC but really any plug and play will work and the Haltech's look like a great setup.

We can build a harness to work with the engine and run the Miata cluster. Can be done in a PnP fashion for just about any ECU.

There's really nothing about the S4 engines that are easier to deal with than the S5. If you're planning on using a JDM pull and not building an engine, make sure you get a warranty and the engine can be returned if it's junk when it arrives. Way too many of those pulls show up as paper weights.