I am very curious about this as well. My kit has yet to arrive, but I spoke with them about this issue. He believes that there is a bad batch of bolts out there, causing some of the issues that a few Turbo builders are having. According to him, he has done all of his testing on several sleds on original mounts, and not broken a bolt to date. I still think swapping to the highest grade bolt you can get is probably a good call. In addition, FTX makes a really sweet looking billet mount plate. I am half inclined to order and install when I put on the turbo, but will probably give the higher grade bolts a chance first.
Another thing I read that a turbo builder did, was fill the gap between the body of the bolt, and the hole in the rubber mount cushion, with silicone. Apparently, there is a fair amount of play between the bolt and the cushion and the thinking was the silicone would dampen the cushion shearing the bolt.