go and find a seat tolado,ibiza, or any with said engine. don't bother with accident damaged ones that seems to make them worth more, just have a lookk at listings for motor auctions and tip up at one with a few hundred quid. the donor car for my conversion cost me £250 it had mot and few days tax left when i bought it. only things wrong with it was a blowing exhaust and the air con didn't work very well.
that way you get to insure the car for a week and rag it about or take it to get a dyno run done so you know if the engine is good before you fit it and and your quite likely to find any issues that need attention so they can be sorted when the engine is out, said cars also come with loads of other usefull bits they really should be called conversion kits