I cannot praise you highly enough for your patience with me Vinny. I naively assumed a SID 801 was a SID 801. The end result though is beyond what I had imagined, and I am still smiling (a rarity for me I can tell you).We really are amazed that your car ran with the wrong ECU in it. The Siemens SID801 and SID801A use a completely different circuit board inside even though they use the same processor and memory etc. Obviously the fuel pump and injectors are the same on the engine.
I did try this myself using the wrong ECU on one of my test cars but it didn't work on that one.
When using an unlocked ECU it's essential to make sure every number matches up, or better still is to send us a photo of the ECU label then we can make sure we have the right one. There are a few engine and ECU variations on the 307 alone.