iMac Intel 21.5" EMC 2544 Adhesive Strips
Place some sticky tape along the lower edge of the iMac either side of Apple logo. Position screen carefully onto the lower ledge and then use the tape to hold. Tape then acts as a hinge allowing you to raise or lower screen while in the right position. I did this and also used some tape at the top so I could reconnect screen and test HDD install. Then you can hinge screen down to remove the adhesive tape backing strips in order to close up the screen for good!!
Very simple so long as you take your time. I had the benefit of an on site screen replacement so could see what the tech did. A few tips inc links to photos.
1. Use a marker to draw a line on the plastic card so you can see the max depth.
2. Use sticky tape either side of Apple logo on the front of the iMac, you can then position and rest the screen on the lower ledge in the right place, hold with the tape (don't remove the adhesive backing tape at this stage). The tape then acts as a hinge so screen can be lowered and raised to refit connectors and remove backing tape. More tape at top will allow you to trial fit and test prior to sealing the screen back on. It's what the Applecare tech did when he changed the screen!!
3. Be careful when removing old adhesive. Screen has a black plastic type backing to it (this forms the black frame that you see from the front) and is easy to peel and damage.