Rear ABS only uses a tone ring in the rear diff with a speed sensor on top of the diff. There's a module in the passenger kick panel IIRC. 4 wheel ABS has tone rings on the front hubs too. The only sign under the hood is if you have 4 wheel ABS is there is a hydraulic manifold/module next to the master cylinder IIRC. But you shouldn't as that was an option on 94(???) up - pretty sure it coincided with the CHMSL tailgate light. For rear ABS, there should be a valve on the inner driver frame rail (with pigtail harness) near the frame axle kickup. There is a bleeder on it that looks like this
Notice the bleeder on it as well for bleeding upstream of the wheel cylinder (I think, it's been wayyy too long) as opposed to at the wheel cylinders which is for wheel cylinder replacements, but it's good to bleed both as you have no brakes... I don't think it's the MC that's the problem btw. Early Dakota rear ABS is pretty not great. If you pull the tone ring (or just unplug the top sensor) you'll get an ABS and brake light, but it will default to "standard" brakes sans ABS.