Hey,
The Blitz kit, isnt just the adaptor plate, it inc everything so its just a bolt-on mod, that is why the price is around the $700.
Also you will need an aftermarket ecu as you will need to run gtr injectors which are larger than the stock gts-t injectors, and if you can get the piping from the plenum side off a gtr that would also be helpful!
I've look into it and the results look good (increase the mid range responds of the car) in the end the cost will be about the same as a greddy kit
$700 for the blitz kit + $300 or so for the gtr plenum