Hi all!
TDLR below for anyone that doesn't need my life story...

Firstly, I know how f'ed the below is going to sound, anyone with suggestions or advice is more than welcome to call me a big dumb idiot...

I'm three years deep into my 180/240sx project and have (metaphorically) hit a wall
I bought my 1989 180sx as a shell and bought a redtop sr20 separately.
The previous owner of the shell (that originally had a CA) did half a SR20 swap and then pulled the motor for another project.
The previous owner of the SR had videos of it running before it was pulled, as far as I can tell it is in working order. I have not had it running since I bought it

Electrical on the shell was an absolute mess, made worse by the fact that the shell was originally an automatic and I decided to do a complete wire tuck and move the engine bay fuse box into the glove box. Thanks to the FSM wiring diagrams and lots of Nicoclub/zilvia posts, I seem to have done ok. However it seems that the injectors are not receiving a ground signal to tell them its time to spit fuel.

TDLR:
180sx automatic CA shell, SR swap with wire tuck - cranks but no start - spark but no injectors fire
Nissian 61 ecu (sr20de redtop/auto)
Injectors pulse when given GND and 12v directly
Injectors pulse when plugged into harness and injector drive pins grounded (101,103,110, 112 fire correct injector as per ecu pinout)
No injector pulse while cranking engine or spinning CAS by hand
Fuel pump primes/powers on while spinning CAS by hand and when key is turned to ON
No injector "batch fire" when key is in start, even with pin 34 (start signal) hardwired to 12v
ECU outputs 12v to pin 101 (injector 1 drive) at all times, including with key off - does not happen to other drive pins (bad ecu?)
Also tested with unknow Apexi ECU - serial PFC SR202R 9709-0041 - no 12v to pin 101 but also no fuel pump prime or spark
Injectors while connected to harness send 12v back to ecu pins (bad?) - no power in signal/drive wire with harness off - 12v constant on power side

Good strong spark to all 4 cylinders (means its not CAS issue?)
ECU pins 107 + 108 (injector ground) show good continuity to ground
New fuel as of yesterday
Intake manifold is current separated from the engine so I can see/smell fuel when the injectors fire - grounds on back of manifold still show good continuity to chassis

I've tried everything I can think of and tested everything I believe I can, happy to take any advice you might have before I go and drop 400 dollarydoos on a "new" 2nd hand ECU or 200 on a CAS...

Thanks in advance!