Use a piece of tape around the antenna cables to keep them in the same order, makes reassembly a little easier.
Two notes here: If you are using OWC’s Thermal Sensor HDD Upgrade Cable, be sure to tuck the cable under the hard drive slightly. You cannot allow the connector to sit near the top edge since this will not allow the monitor to sit flush with the chassis when it is reattached. Additionally, the SATA connector does not seem to fit together as snuggly as when it was connect to the HDD, so tape or a plastic cable tie to keep the connection tight may be good insurance to prevent it from coming loose.
If you are planning on dual booting with Windows 10, the Windows 10 installed failed when the SSD and HDD were both connected at the same time. I had to disconnect the HDD until Windows 10 was installed. Note: I did a fresh install on a new SSD not configured as a fusion drive. If you are planning on doing this as well, use packing tape (or something similar) to hold the monitor in place until after installing the OSs. Then reconnect the HDD and apply the adhesive to the monitor for a permanent seal. Good Luck!
Continuing from my previous comment. To remove the adhesive on the right side you’ll need to create a very slight gap to give the pizza cutter some more room. Do this by cutting the adhesive on the left side up and around to the camera. Before attempting to cut the right side. Carefully slide the plastic cards (I purchased two sets) to ensure the adhesive on the left top and side is completely free. Now slowly move towards the right side. After every inch or two of removing new adhesive, slide the card over to create this slight gap. Be careful to not move the card too close to where the adhesive has not been cut. You want to create a very slight gap without creating too much pressure. Use extra caution with approaching the areas where the antenna are since the adhesive is stronger here and will need some additional cutting. Follow this approach all the way around the right side. Be careful to not create too much pressure at any one time. Good Luck!.
Removing the original adhesive is easier than removing newly applied adhesive (e.g., if you have to reopen iMac). If you should happen to need to reopen the iMac, please use extreme caution and highly consider my suggestions below.
When using the pizza cutter tool, do the first few steps in reverse starting with step 8. Starting on the left side is better since this is where the adhesive is narrowest. The right side has two antennas and the top right has one, see the pictures for step 18-21, they are the brass colored metal rectangles near the edges. The adhesive on these pieces are wider and therefore have more holding power. The thickness of the pizza cutter tool is enough to crack the glass.