Standard disclaimer: You are better off buying a Punto Sporting or GT (P.S. the GT is an 8v)
Right, now that's out of the way, let's get down to details. It basically boils down to cost. The GT is going to be more expensive to convert, more expensive to run, more expensive to insure and less reliable. For GT power levels and engine weight, you pretty much have to do a full GT conversion, steering, brakes and suspension too. Consider that GT engines are now getting old, and a lot will have been abused. Unless you can get mates' rates to have the head checked over, and reconditioned if necessary (GT heads suffer many hairline fractures), you should factor regular head-gasket failures into your budget too. As well as a possibly worn turbo and fuel costs, there is also insurance costs.
Your engine choice from the Sporting seems like an odd choice. I assume you have a mk1 of course (otherwise completely rule out the GT conversion). The reason I say that it is odd is that the mk1 didn't have a 1.4 16v engine fitted to any models. The Sportings were powered by either the 1.6 8v MPi unit or later models were powered by the lighter 1.2 16v MPi. Due to differences that may exist between the mk2 1.4 16v and the engine mountings of your car, some custom fabrication may be necessary. If this is the case, it is likely to be expensive. Perhaps you did mean the 1.2 16v unit. If so, it is still recommended to uprate the suspension and front brakes. In fact, since it is almost as expensive to do a Sporting front brake conversion as it is to do a front GT conversion, you may as well have vented GT brakes at the front. The current 240mm x 11mm solid discs just will not cut the mustard with the extra power.
