just so you dont have to just accept that you can not do it i will elaberate slighty just for your infomation...
one of the main problems with turbocharging a na is that the na will run at say 170psi compression on each cylinder, wheras the coupe runs around 150psi, no i know those figures dont look a million miles away from each other but that is without the turbo spinning, once the turbo is spinning that psi mangnified greatly.... I dont have the exact figure to hand but say for arguements sake its x3 , that makes the coupe engines compression at 450psi and the na's with a turbo bolted to it 510psi, so youbasically blow the car apart
you can reduce your compression rating by using things like custom made head gaskets but its not worth considering when you could source an entire 20vt with everything there for less money.
Supercharging, it is feasible, although again too expensive, you can use an eaton superchange and use it where your air con compressor is (if you have one) but then you run into problems with the exhaust manifold... the list goes on...
Hope that helps abit more then just no
however i still agree with them, just get a coupe lump and drop it in or even just get a coupe, i did
2xHLX owner,3xHGT, (then the darkside) 1xCoupe20vt now the proud owner of a Black Coupe20vt LE!