On my 74 2.0L, the rear sway bar link (drop link) is disconnected because it appears some plastic piece broke.

Where can I get this piece (circled in attached pic)?

www.pelicanparts.com

GPR

Any number of places. Rear Drop link bushing.

buy the set. replace them all. while you're at it do the ones where the bar mounts to the trunk floor.

And to answer the question you'll ask when they arrive from whoever you buy them from, drill or poke a hole through the center of the back side (outboard as installed), fill the cup with a good waterproof grease, use a vice or vice grip to slowly press in place.

Credit to McMark for the methodology.

You are reading my mind.

another technique I used was using a camp stove in the garage with a pot of boiling water, to literally boiling the plastic cup one at time, and while leather wearing gloves, you can press fit them on the drop link without any tools, first I assembled the cups on the drop links, by boiling one of the cups at a time, pull it out of the boiling water with a pair of tongs, then you press the one cup at a time against a tabletop, (make sure you get the correct geometric relationship of the cup openings correct - visualize how the drop link appears after its installed). After you have the drop links assembled, you boil the whole assembly in the pot of water, then in the time of less than two minutes, you pull the link out of the hot water and snap them on by hand and channelocks. Also have grease ready immediatelly before you mate those cups up with the end of the sway bar and the bottom strut bolt. The preferred order is the sway bar first, then you can press onto the lower link last. You will be surprised how pliable the plastic is after its boiled. After about five minutes, it hardens itself back to the rigid plastic. I got my bushings from autohausAZ.com. part number 90134378200
good luck. I posted this technique this past year but cant find it.

Not a problem. I have to read Yopu's mind all the time.