I just did a little more research on this, here's what I found. From the factory, our car's ecm has no control over ignition timing whatsoever. The whole system is contained within the distributor. So, if you replace the ecm with a standalone, you still have nothing. However, if you look at the same year Miata as the Capri you have (in my case, I'm looking at a '91 Miata), the ignition system is different. The ecm sends out commands to fire spark on cylinders 1 & 4 together, and 2 & 3 together. It's a waste spark setup. Due to the design of the engine, when cylinder 1 is at (or near) top dead center on it's power stroke, cylinder 4 is 360 degrees out of sync, on top dead center on it's exhaust stroke. 1 and 4 fire together, so cylinder 1 will do it's thing and produce power, whilst cylinder 4 will just waste the spark since there is no fuel in there. Cylinders 2 and 3 are 180 degrees out, and are each 360 degrees out from each other. So, you've got a factory batch fire/waste spark setup that is controlled from outputs from the ecm. Perfect.
My assumption here is that if you took the 2 ignition coils from the Miata, and likely the spark plug wires, then deleted your distributor, and then replaced your ecm with a stand-alone that could give out those spark commands, you should be good. The commands are looking for both crank position sensor inputs and intake air temperature sensor inputs, which is why the folk's gave me part numbers for those in the email. You'll also need a way to measure incoming air, and we have that silly VAF thing, but what you really want is speed density. A MAP sensor. With a stand alone, you can get rid of the VAF and build yourself a nice cold air/short ram intake, hook the MAP sensor into that, and voila. No more VAF, no more distributor, no more weak and stupid ignition system.
It SOUNDS easy, but I don't know. There's no step-by-step tutorial for doing this, so it's going to be trial and error. That's why I'm still on the fence about it. I might try it, I still don't know. It'd be about $800 USD for everything you need, including a wideband and AFR gauge, to datalog and tune your car. Doesn't seem crazy steep for the amount of power and control you'll be able to get out of it, but it's still a lot of money for something that's likely to be a pain in the ass to install.
Let me know your thoughts. If you want to try it, I'm willing to give you all the help I can. You can be my guinea pig lol. If you can make it work, I'll probably follow suit. If not, $150 for a Rocket Chip I can replace in 10 minutes is sounding quite tempting.