problem with 94 jetta

so i let my lil cousin borrow my 94 jetta the other night and well the battery died on it so he said he went to his friends house to use his 97 jetta battery to put on mine so we could get home so anyways he connected the battery wrong positive with negative and vice versa
so now the car wont start it sounds like it just cranks
i checked the ecu and i opened it up and it is all messed up
so my friend let me borrow his ecu of his 97 jetta
but the samthing is happeneng like it just cranks but no spark
can anyone help me o tell me what else i can check
could it be the 97 ecu not working on my 94??
anyway to check if the ignition coil blew too?
any help is appreciated this is giving me a headache =(

no one has any help for me??