Imports from Japan are "Fairlady", "S", "T" and "ST" models - "S" will have the sporting aspects of a UK car like the Brembo brakes, "T" will have the luxury aspects like leather, cruise and nice stereo. Only "ST" will encompass all the aspects of GT and UK spec.
Ask about delimiting and speedo conversion - has the trip computer lost any functions as a result of conversion? Don't pay extra for Sat Nav you can't use and a nice radio that doesn't cover the UK bandwidth.
Early imports have different plastic grades and feel slightly cheaper than an equivalent UK car. Suspension may feel rough by comparison. All improved on '05, I believe.
Look out for tyre feathering on the front or unusual tyre wear patterns. Listen for clunking rear axle outer bearing and roof seam joint movement noise. Check all electrics for correct operation. Ensure clutch is good (if manual).
Be aware of possible aftermarket modifications and ensure you get relevant documents for operation / installation of anything non-standard, e.g. adjustable shocks, performance exhausts and filters etc.