It's a great idea, the 1UZ is a nice little engine, but you may find yourself hit government regulations on the size of the engine you can put in the car, a 4L V8 is a big step up from a 1.8 or 2L. It all depends what state you are in really.
its weight thats the determining factor not factory engine size
in NSW cars 1100kg or over (ie 85 celica) u can put in a
weight x 4.82 = N/A engine of your choice (in cc)
weight x 4.0 = F/I engine of your choice (in cc)