For pipes, use silicon hoses such as samco's or other alternatives.
In the s42 touring car they used an external expansion tank located behind the exhaust side turret. Checkout swiss's thread in the general section as there are lots of pictures of it there.
Do you have your radiator out already? If you could get the dimensions of it for me im sure i could find you an alternative to the ireland engineering one, such as the radiator out of the integra type R.
You need to find out:
The distance between the two lower mounting holes (center to center), The width, The height and the thickness.
If you are going to run an external expansion tank and use custom silicon hoses then the location of the inputs and outputs arent that important. As long as they are roughly in the same place so as not to affect flow.
Think about it man, we could be innovators, showing people a cheaper diy method. Kinda like how the Honda crowd discovered that they could swap in the Accord's radiator into their civic and almost double their cooling power.
Its kinda lucky you posted this thread up because i was about to do the same.
If you arent bothered measuring il do it if i have to...but im not sure if the dimensions are the same for the E30 and the E36!