Hi Ollie,
All the engine bolts should interchange but thats about it except for common fasteners. 
Some accesories will also swap across too , ,but there are still plenty H parts about if you know where to look  
 
With any bike you have to check for oil leaks, engine and suspension , brakes , tyres (creep) , crash damage repair , bent bars , bearing play.
The less details you get about servicing and paperwork showing it the more you have to scrutinize the bike, if the seller is genuine they wont mind and should be keen to help to show the bikes a good un , if a seller is rushing you on the sale - be warey as most likely don't want you finding anything wrong with it. 
A test drive is alwways a good idea but more and more sellers wont allow unless your insured or put the full amount of cash down as a security. The two bikes I bought here I never test rode and only the ZRX I heard running before buying.
Your always going to find faults or missing parts, it's the nature of old bikes but if it's been well looked after you can still find gems.
Good luck on your hunt,
MM! 
