Formula 50 LC head gaskets

1st off, will the 68cc gasket set #M119788C, fit a stock engine? I've lost compression in the engine and don't want to open it up without gaskets. Not sure if it's rings, cylinder, or other problems. Last year it was 110psi and now it's 90psi and I'm not getting a vacuum through the carb. 

From what I've heard, the AC and LC pistons are the same, so finding 1 isn't that hard. Finding parts to the big bore kit is easier, but I don't want to upgrade everything right now. I've had a problem with the exhaust gasket, but I hear that's kind of common with these bikes. 

Any help you guys can give me would be great.