The OP didn't want a Stroker. You guys can spend money for nothing right quick.
Bob weight is overrated. By a long ways. He can get a different piston, but it will be hell to get quench. I'd have to pull my bob weight card, but I don't think my Pistons were anywhere near 850 grams.
The point is...the OP has the Pistons. There is nothing wrong with them. In fact, I can make the argument that he may be going backwards buying a newer piston. Especially if that new piston isn't designed to come out of the deck.
Old doesn't mean bad. New doesn't mean good.