Been a few months since I've posted an update. Came home a few months ago and the Uno was running lumpy. After checking everything I couldn't find the culprit until I started to tear it apart. I found this:
Took this as a sign that I am meant to complete the P60 upgrade. I got all the bits in but obviously it wouldn't start without disabling the immobiliser first. I've had 2 auto-electricians helping and none of them have been able to crack it yet. Starting to think I should have looked a little harder for an MK1 engine instead of going with the MK2
I've got the engine cranking, the injectors pulsing and the fuel pump priming but until the immobiliser is disabled she won't be firing up. If I'm not able to resolve the immobiliser issue I'll have to install the code-box etc. which I was hoping I wouldn't have to do.