Great thumbs up for very hi-res photos for this section. This thing was THE hardest in this guide. If you haven’t got courage to do this, just buy the one with bracket. Even if you have - zoom into the picture. It will save the day.
If you have hard time putting the cable back into the ZIF connector, try gently pushing the cable down against the bracket while pushing it into the connector. Simply pushing the cable into the connector doesn’t seem to work well.
Are you trying to take the optical drive out entirely and install a new HDD there? You need an HDD bay (mounter, adapter, whatever you call it) for your new drive to install it because: 1. HDD is way too small to fit the place and 2. the connector for optical drive is different from that of your HDD’s.
If you don’t have any, iFixit offers this (careful, it supports HDD up to only 750GB!)
If you have one, did yours come with some instruction to secure your HDD in place? Follow the instruction on that (usually requires you to put 4 screws on the side of your HDD as well as to screw the metal part you scavenged from your SuperDrive.) Once you take out the SuperDrive, replace the words “optical drive” in this guide with “your HDD bay,” then backtrack the guide (in fact, most of the guides here only instruct you how to disassemble your device; There’s a final instruction on the blue area to backtrack the guide to assemble it back.) That’s what I did.