When swapping engines from one type to another the least expensive and least frustrating path is to buy the model that came with a V8 from the factory. I would recommend selling yours and buying a 2006-2010 4.6L 3V V8 model. Preferably a 2009-2010 model year if you can find one. This way you end up with 50+ more horsepower, more torque, better gas mileage and a 6R60 or 6R80 six speed transmission that is vastly more reliably than the 5R55 in your 2002.