Since I no longer needed the pistons from the 2.8L engine, I decided to pull them and sell them on eBay.
Important: Remove the Pistons and Liners Together
Here's where I went wrong, right off the bat: You must remove the liners and pistons as a set. I didn't know this -- I removed the pistons alone. This was due to my naiveté, not realizing that the picture on the DeLorean store for "Piton and Liner Assembly" was showing only a piston head.
Removing the Crank
With the lower crankcase out of the way, the bottoms of the connecting rods are clearly visible. To disengage the rods from the crank, you simply remove the two nuts holding each in place. Then you need to separate the two two halves of the rod. I found this somewhat troublesome, and had to use a pry bar to carefully split the two apart. I was then able to slide them off. There is a smooth metal half-ring sitting inside the rod; this the is connecting rod bearing, make sure you don't lose it.
You'll be able to get a few of these apart pretty easily. To get to the rest, you'll need to rotate the engine with a wrench on the main pulley nut. Be careful not to jam any of the rods against the crank as you turn it; go slowly and carefully move the rods out of the way as you work.
Once all the ends are removed, you can lift the crank out. It's heavy, around forty pounds, so be careful.
Removing the Main Pulley Nut from the Crank
Now I had a problem: I needed the nut on the crank to turn it so I could align and remove the pistons, but now I couldn't get the nut off. I couldn't find a way to brace the crank so that I could get enough torque on the nut.
I finally put the crank on my workshop, under a few pieces of wood to raise it high enough that I could clamp the nut in my bench vice. I was then able to slip a socket on an extension into one of the holes in the crank, then slide a piece of pipe over that and turn the entire crank, breaking the nut free.
Removing the Liners and Pistons
With the crank out of the way, you can remove the liners and pistons. Again, I did this wrong -- I removed just the pistons, and then the liners. If you do this for some reason, be sure to mark which cylinder each piston and liner goes to -- which I also didn't do.
To get the pistons out of the liners, I was mostly able to wiggle them free. In a few cases I had to carefully tap on the ends of the connecting rod with a hammer, but I got them all out.
Only later did I removed the liners. Supposedly you can twist and wiggle them out, but that wasn't working for me. This worked pretty well -- after a few taps that side started to slide out. I repeated this on the other side, and eventually the liner fell out the top of the block. There are some small dings on the bottom of the liners from this, but they are quite minor and won't affect sealing or piston movement in any way.