you should probably drill the holes on the back top corners of the tank, and not on the bottom just incase the power goes out.
Thats what overflow covers are for. Water flows over the top of them, and when the pawer goes out, water cannot keep flowing over them.
Marowana420, i would go with an overflow in each corner. If you put them in the bottom, you'll get more flow out of them, but will need to add overflow covers as well. With 1.5" bulkheads, tyou'll get a flow of around 1350gph out of each bulkhead... if you put them in the back wall, the flow is alot less as you wont have gravity on your side. The flow threw 1.5" bulkheads in the back of the tank will be around 844gph each....
so it really depends on what kind of turnover you want on that tank, and what size pump you have.
If you put them in the back wall, the apperance is more sleak, with out the over flow wall.... if you put them in the bottom, you'll have to install an overflow wall and stand pipe. Or you can just go with the standpipe and no wall, but that doesnt look that good.