being in oz i presume your motor is the kv6 lump so for info on rebuild and go faster tips try some of the rover mg forums as for alternative engines well how far do you want to go unfortunately you dont get the diesel version as that is the swap i would go for another possibility is the v6 mitsi lump as the newer sedonas use but how about going totally beserk and fitting a monaro lump

any engine can be squezed into any car its just a case of how much work you are prepared or capable of undertaking i have seen pictures of a v8 chev in a toyota mr2 and at the moment i am helping with fitting a rover mgf lump into a lotus esprit (and that is a real can of worms)
ttfn glenn