Remove 2 L shaped side brackets and 1 bottom bracket. Each bracket is held in by 4x T10. 2 side L bracket have sticky surfaces on the inside making it very difficult to pry off (use very thin metal spudger). Sticky surface is against the thin foil tape so it may scrape off some tape (its okay, need to peel it off anyways)

Note the picture shown with brackets removed has the foil tape already removed

Utility knife is better. See next step on iMac for reference.