M5 turbo questions

[e30isking]

Hi,

I am going to turbocharge an E34 M5 with holset HX55 I found very cheap.

For those that have done this, what is the best Intercooler size to get 600x300x76 fits well? I will remove AC system

Also can I fit 3,5 inch exhaust without moving the ECU?

Thanks from Portugal!