If the case is aluminum, you'll be able to get the bolts out with no effort if you use some heat.

If you have a torch, then heat the bolt until it's nearly red hot. Then use a bit of penetrating oil such as Kroil on the threads. Apply the Kroil again in a few hours and allow it to work for about 24 hours.

The studs should easily be removed with vice grips.

Just be careful to keep the torch away from the aluminum.