I'm not familiar with the Dakota's.
My 1949 Dodge truck I installed a early 90's Toyota Corolla MC ... simply because it is a upgrade to a dual pot instead of a single pot .... it shares the same odd 3 bolt mounting. So it is a easy conversion.
When ordering it .... in the 90's ABS was a option on the Toyota anyways .... I chose non ABS for my needs.

All I'm saying, just because it was available does not mean you have it .... A quick search on Rock Auto to see if you have a choice between ABS and non ABS may give you a clue if your truck automagicaly comes with ABS.

My 1991 Chebby truck has rear wheel only ABS ... I honestly do not know if it was a option or mandatory .... never needed to work on them.

 

On the rear, there should be a single sensor on top of the pig.

No sensors up front does indeed mean 2 wheel abs, should be just a dump valve plumbed into the rear brake line. (aluminum block with a couple solenoids on it.)

 

Yeah I’ve always been confused about what sort of brake system this thing has lol. I don’t recall seeing a sensor but what is the “pig” you speak of lol I haven’t heard anyone use that word to describe something on the truck.

Peaking around RockAuto, the master cylinders don’t specify with or without ABS, seems like they’re all generally the same. But there are ABS parts that you can buy like a controller and hydraulic module, etc.

 

I've had my 88 for 8yrs,also have a 94 sport and o3 slt and have done mods too them all and the most significant change that seperated the 88 from the others was done for performance and this was a side effect. I put a ford explorer 3:73 rear axle in it and had the salvage guys take care to save all attachments so it bolted up with no issues other than special u-joint and axle tube u bolts. But that isn't the story you wanted to hear. When I went for the first ride I noticedI had to learn how to drive my truck again cause now it would S T O P !!! And no bs it was a different truck! You don't have to do it my way but the problem with dakota's is no rear brakes! If you put rear disc on it and get the master cyl for rear disc it will make your passengers wear seat belts lol. But thats just my personal exp with the 8daks I've had and 3 I still do.

 

Mine is a 87, it came with a different type of rear anti lock. It used a contraption that bolted to the rear leaf spring. 1 line fed fluid in, and it was supposed to decrease the brake pressure as the rear lifted. Most all seize up and they are not available. In short I took it off. However this did not make a difference in the truck, as far as I could tell.
Latter, I installed an explorer 8.8 with disc. The truck stops much better, and the pedal starts working sooner.


Edit to add, you may be better suited with a 9.25 dakota rear...... It would keep the 6 bolt wheel pattern that you have now.

 

The part of the rear end housing where the gears are. Rear wheel speed sensor reads a tone ring bolted between the ring gear, and the carrier.

 

If you have the manual it is chapter 5 page 41 if you don't the 95 manual in the FAQ is chapter 5 page 44. The picture shows the main components, the speed sensor goes into the top of the differential (pig?)
The only replaceable in the driveway thing I have not replaced on my 94 brakes other than the hardlines is the module and the antilock valve which mounts as hey you describes after the master cylinder.
I reread some of the thread and I am not sure you get better vacuum to the master cylinder the way you say you hooked it up. Try putting back to the OE nipple for it and see if that has a desired effect.