In addition to ok4450’s sound advice, I want to add another caveat just in case the OP does decide to go ahead with an engine transplant.
Installing a different design engine in the vehicle would also necessitate installing the correct Engine Control Module (ECM) for the new engine. And then, there is the question of whether a different ECM could communicate properly with the original Transmission Control Module (TCM) of the Rover. Most likely it could not interface properly, thus leading to extreme shifting problems.
Unless the OP wants to gamble on a rebuilt Rover engine, the only practical course of action is probably to sell/trade-in the vehicle.