I'm using the original ecu out of the mitsi. Can I run the mitsi ecu without the cas unit?? This is the last thing I have become stuck on so would love clarification. I figured the ecu would need it to know injector timing??

You can try it. If it is batch feed injection, it may work. But I think it needs the CAS sensor for signal input to activate the fuel pump.

This Nissan Optical CAS fits right in the A-series block. Swap the Mitsu optical wheel as it has a different pattern.

So is that the dp4 dizzy? What model cars do I find it in? Only turbo, or any sr20?

In the EXA turbo. In N12 with E16 engine.
The E-series D4P fits in the Datsun 1200 engine block. There are many D4P like Honda, but they don't fit the A-series.

I checked out a gtir pulsar today which is an sr20det and was a d4p dizzy but the internals were a bit different to the e15 ones. Would an sr20/det dizzy work, or only e15?

I believe it needs mods to work in an A-series. One is for sale at FS - Sr20 crank angle sensor to suit a12

His dizzy only has two wires coming out but has the cas in it, shouldn't it have four wires? And no dizzy cap and rotor so I'm guessing it was set up with individual coils. It may fit a cap and rotor on it though. Not sure