Just a question about the engine, have you had the engine number checked against the rego papers? Is it the original engine? Just because the VIN says it's not a 195 HSV engine doesn't mean it hasn't been changed at some point.
Just saying.
A lot of the time a buyer will blame the seller when certain things are discovered to be not up to scratch on a car, but (and I'm not saying this is the case) the seller sometimes doesn't know this so they are selling the car in good faith. Although after seeing there is some history on the forum about the car the seller knew full well what he was selling.
A mechanic is in business to make money, some are more thorough and will pick a lot more than others. It is in a mechanics best interest to pick as much as he can to repair to make money. A lot of the repairs pointed out may not make the car unroadworthy, but still need repairing. You can't put all that on the seller. As said, it is up to the buyer to get the car inspected before the sale so he is aware of as much as possible before he parts with his money. The only thing you may have recourse on is the fact that he advertised the car as something it was not. Not the fact that you bought it as an SS, that is your problem for not checking it, legally, the issue is what he advertised it as. He may be able to be charged with an offence for that, but I don't think you can claim any compensation from him as you weren't really out of pocket by the fact that it isn't an SS. By all accounts, a Berlina is spec'd higher than an SS anyway, so you actually got a better car model wise.