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NeilVox Ok, I have some advice for you and you may want to listen as I have an MPi Sei and it has a P75 engine fitted, in a fashion, Don't do it! just fit a 16v, with out going to great expense you wont get it running right. Please I am trying to give you solid advice here.
The issues come from the PowerSteering as it takes reading from the ECU for speed due to it being speed Variable, now with that in mind the only option you have is to piggy back the P75 ECU onto the Stock Micro ECU, or go full Stand-alone, if you run the P75 Piggy Back you will need to cut and splice the cars loom and a P75 loom together so it can be run, now if you run the 1.1 engine with the 75 head then you will only see a gain of about 5-10 bhp but you will need to modify the loom as none of the plugs for the Sei loom will reach to where the sensors are, if I remember right there is also an issue with the fuel lines too but I think that's easy fixed.
Now you could in theory run on the stock ECU with the 75 head and plastic inlet but again, this is the set-up I am currently running and it Dyno'd with the 1242 block at 69bhp, I had better out of my old 1.1spi.
Now with all this that you are looking at, look into a 16v conversion, its a lot easier and the gains are bigger.
If you are like me and want to stay 8v then I will actually help you how I can as I HAVE done this conversion but knowing it I really wouldn't recommend it and would strongly recommend a 16v conversion instead.