Front fenders on all cars are interchangeable, all dash boards are interchangeable (unless RHD obv.), grills, hoods, trunks, sun roofs, aluminium bumpers swap to plastic bumpers lots of people do it its not that hard, front valences swap, doors on all 2 door models swap however they don't swap with 4 doors (obv.) however that question has been asked before. Suspension is all interchangeable except for "IX" suspension and for that matter the IX's drive line is totally different. The LSD's out of "IS" cars are interchangeable with the regular open diffs. seats are interchangeable a common swap would be the stock seats for the Recaro seats out of an "IS" version. All parts from 318's 320's 325's 316's are interchangeable. If its an e30 you can mix and match pretty well everything to make you own pride and joy. If you are looking for information your best bet is to use the search option on here, e30tech, bimmer forums, and rv3, because chances is that it has been asked a million times before and there is already a thread about it. Welcome to the world of E30 and hope you enjoy your new project!