The ultimate cost of purchasing and correctly converting a [NA | 2+2] to a Twin Turbo setup will far exceed the price of purchasing a Twin Turbo in the first place. There are a multitude of parts which must be swapped over, from fuel pumps and associated computers to EFI harnesses, etc.
Some of these parts may come with a J-Spec clip (should you choose to go that route) however some are LHD specific and will still have to be sourced.
I would encourage you to look in the classifieds forum on twinturbo.net, cars.com, E-Bay and your local Auto Trader. A variety of Twin Turbo 300ZX's are always for sale.
Sincerely
TwinTurbo.net
"boobies have power" - Bernie(NoVA)

1993 Ultra Red Z32 TT Convertible
1997 Black XJ (2+2 4WD 4.0L)