Just did my own last week, ive got an R32 cooler which is slightly bigger than the R33 one, but the out/inlets are the same size, they are 3", but i got 2.5" piping from then on, i just got the 2.5" pipe enlarged at the tip to 3" and welded a 5cm extension of a 3" pipe to connect up to the cooler. bought 3" hose from Pirtek and some T-bolt clamps.
I doubt very much you could fit a pipe bigger than 2.5" as it wont fit between the fan and the timing belt cover, unless you have a modified intake plenum, then you could go 3" all the way...
All up it cost me $350, for stainless steel pipes, clamps and hose, did the rest myself
good luck...