1988 Porsche 911 wrong battery installation and failure to

Not sure what is damaged without a physical diagosis,but there can be several things that can be damaged,but first check all the fuses and replace if nec.Have someone crank the engine over while you check for spark.Also can you hear the fuel pump running while cranking? Its located up front under the fuel tank.The engine control unit may have been damaged and that will keep it from starting.Also the alternator can be damaged but you won't know that until you get it running and check the charging system.