I guess I've never seen an 8" without a drain, but since they are so easy to pull the pumpkin - drive shaft, 4 nuts at each axle, 10 around the circumference and out it comes.
I truly hope there is no crud on the bottom. If there is, it WILL get expensive - soon.
To put a drain in the bottom, you not only need to drill the hole, you need to weld in a 'bung' for the threads. That housing is sheet metal, probably about 16ga. Ford punched a hole then threaded the raised steel on most of their rear ends