As everyone else said, it can be done, but it is not easy.
With that said, I'm in the process of doing the same thing myself. (well I spent a lot of time working over the summer on it and am now back at school without access to my d44 or tools). So I'll share my experiences with it.
Keep in mind I'm converting to disks at the same time (using crown vic parts).
I brought the dana 44 shafts and Dana 35 shafts into a local auto shop to get the bearings pressed off and the tone rings off of the 35.
Brought the 44 shafts and tone rings to a local machine shop (and lucky me, the guy was a big drag racing fan, knew a lot about axles). He machined out the center of the tone rings to 2" diameter, and LIGHTLY machined and radiused the area where the tone rings get pressed onto the shaft. That was just because it's a very rough and unever spot, and otherwise impossible to mount the tone rings.
The tone rings were machined well so i could tap them in place myself, and I got the bearings and other stuff pressed back on. Unlike three of the three auto shops I talked to in the process of doing this, the owner of the machine shop told me the tone rings are NOT "pot metal" and were easy to machine without worry about breaking. The machining cost me $50, which completely shocked me, as I thought it'd be far more expensive.
The only other thing to worry about other than getting the tone rings in place is to mount the sensors in a position where they can read the tone rings.
Let me tell you this is NOT easy as there is very little room, and of course the crown vic parts didn't have a mount for the sensors. I never finished building a mount, but I did manage to cut/drill enouhg of the backing plate out that I'm ready to build a mount and the sensor WILL work. This is how far I got before I had to go back to college.
In hindsight there are a couple of things I'd consider doing differently. 1) I think the amount of work necessary to use the crown vic brake parts is similar to mounting ZJ disk brakes. With that in mind, ZJ disks have some provisions for ABS sensors, and although they may still not line up perfectly, it'd probably take less modification than my poor crown vic backing plates have put up with. 2) I am planning to mount the ABS sensor in the same orientation as a stock ZJ or XJ. One possibilty I thought of after doing all the cutting on the backing plate is to mount the sensors rotated 90 degrees. This might not make a lot of sense right now, but the ABS sensors are tall, and have to fit in a very tight space, with a wire that doesn't felx well. I think rotating the sensor would help the sensor fit better, make it eaiser to mount, and help clear the wire a lot better.
I'm not sure how adding ABS to the stock drums would work, since almost every part of my 44s drums were shot, I decided to switch to disks.
So to sum this up, you need 2 things for ABS, mount the tone rings, and mount the sensors properly to read the tone rings. Both are possible to do, but the sensors themselves are not easy. I wouldn't change a thing with the way my tone rings are setup, but I'd think twice about the crown vic parts and sensor mounting.
I'd take pictures for you, but as I said earlier I don't have access to the 44 for about 2 months.
I know this is a lengthy post, but I spent alot of time working on it and wanted to share my experience (especially since everyone I talked to said don't bother with ABS, bah to you
).
~Brian