Dude! Your Z is awesome! Where did you get a RHD from?
it's over 25 years old. So no restrictions on import and or DOT compliance. Just fill out the proper deregistration papers in Japan, ship it, file the DOT, EPA, and NHTSA exemptions at a US port; pay 2% Duty and get your bond release. To get it California legal I just needed a Federal motor that I put an EGR and California catalytic converter on that will pass 79 emissions. Sent it to DMV and CHP inspection and done.
Granted I have been doing this for so long I can buy foreign cars like other people buy a used car from a friend so it may be more difficult if you don't know how to work through the system.