Don't have PC version here so can't help you...
But, really, keep trying. I beat the mission, its certainly doable and im no GTA expert. For a game like Vice City it would be much more satisfying to do it yourself, I'm sure you're aware of this and its a last result anyways, just saying...
Unfortunately I was never able to complete Vice City for PS2. I got quite far twice, yet each time my games save mysteriously got corrupted. I'd load the game to a black screen... I believe i could hear sound, just no visual at all...:/ Dunno if I need a new memory card or not but I got too fed up with it to care to be honest.