I wouldn't worry about the stock case. If everything is mounted properly, you probably won't hurt it. In my opinion, the stock 1.76 gears are marginal at that power level. I run a stock case, stock 1.76 carrier with 1.80 straight cut gears in my SG Vette with a 522 and am not worried.
Aftermarket cases are nice, strong, heavy, and don't require shields. If my budget would allow, I might get one, but it's not a necessity...
Johnny