It may be a silly question but if you re going down the 4 pot route would you not be better going for an 1.8T lump out of a passat or Audi? Serious bhp can be gotten from these with little effort...

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"Earl" 1998 2.8 V6 Cabriolet
"The Duke" 1997 2.6 V6 Cabriolet (Sold....sadly)
Project "Best of Both Worlds" 1995 S2 Quattro Cabriolet