Here's a picture of my truck. Disc/drum vehicles always have a mc with a large bowl in front for the discs and a small bowl in rear for the drums. If you have a 50/50 mc, then somebody put the wrong one on. In my pic, you can see that the big line that you're talking about is definitely for the rears while the smaller line is for the fronts. I may have a little bit better pic somewhere if this one doesn't help.
