I asked the very same question a few months ago, and here is the thread that deals with it:
http://www.betaboyz.myzen.co.uk/forum/index.php?topic=3076.0Depending on age of i.e. engine, it may have extra pulleys for power steering (mine did) and the oil filter housing was also noticeably different. On i.e. models the distributor drive is off the end of the exhaust camshaft, while on carb models the dizzy is block mounted. I also found small differences in hose size for the crankcase breather, and obviously the inlet manifolds etc. are totally different. Gearbox dipsticks are very different (i.e. ones are much longer) and the orifices they fit into are differently sized. If I can think of anything else I'll post it up.