Structure is everything - it is easy to check bodywork an dinterior, but don't buy a Z unless you spend a lot of your time looking at chassis rails, floor pans, inner wing flitches, inner rear arches, rad support panel and bonnet support panels. Don't expect to see many Zs without repairs in these areas, but look for quality of repair - have new panels been used or just patches with spots of weld? Have chassis repairs been made with long runs of continous box section or a series of little patches over many years? In other words, has any necessary restoration been done properly or just with a view to cheapness?
Engines are pretty bullet-proof and shouldn't be rough or noisy. Gearbox synchros are quite weak, so check 1 - 2 upshift and 4 - 3 and 3 - 2 downshifts carefully. Try selecting 1st, then selecting reverse to check for movement of gears on the shaft - this should be a noise free and non-traumatic experience.
Body repairs - do sills still show correct body to floor join and seam overlap of rear wheel arch repair? Have rear wheel arch repairs been slapped on over the old rust? Were the inner arches repaired before the outers were added? Did the subtle swage line along the rear body get obliterated? Are replacement panels all lined up with good panel gaps? Any fibreglass panels? All badges and stainless trim present?
Interior - most vinyl and plastic parts available for 240Z and some 260Z, but not cheap. Figure between £40 and £100 a piece for missing or damaged interior panels and over £200 a pair to sort out knackered seat vinyl.
Not obtainable: roof skin to replace the sunroof fitted in the eighties, inner wing flitches, rear quarters hard to get, front valence in original metal hard to get and expensive, new rear lights, wing repeaters. Door skins, radiator support panel, air tubes and rear panel now only available as expensive repro panels. Anything can be made if you are prepared to meet the cost.