Center well on the window and mark an outline of the well 12 inches wider at the foundation and about 4 inches wider at the back of the well. You need enough room at the foundation to use a drill with a 6 inch bit.
Dig out hole at least 1 foot below where the window will be. Using a level mark your rough opening dimensions on the block wall. This window is a 28 1/4 x 48 1/2 Jeld-Wen casement window, so the rough opening dimensions are 29 x 50. Give yourself a little extra room on the bottom to maneuver your window frame into place. Hang poly on the inside of the room you are cutting to prevent dust from going throughout the whole house. Hang a fan in the existing opening to help keep the dust out of the house. Using a 14 inch partner saw, cut the lines you marked on the outside of the house. When the cuts are complete take your level and mark your line on the inside of the house. Using your partner saw, cut through the foundation.
Knock out the foundation wall with a sledgehammer from inside the house so that the block does not damage the flooring. Once the hole has been opened, core fill the block with cement to insure a solid foundation to install your window frame on.
Insert your 2×12 treated window frame, level and secure to the header with ACQ approved fastners. Install 3 inch or longer fastners through the bottom of the window frame into the cement. Now wrap the window frame with Flex-Wrap starting with the bottom, sides, and finishing with the top. This is to insure that if water ever did penetrate, it would flow down like siding on a house.
Install window making sure there is an even gap between the window sill and the treated window frame on all sides. Secure window with galvanized nails and wrap the window fin with a protective tape to ensure no water penetrates. Again, start at the bottom, then the sides, and finish with the top, just like siding a house. Next, insulate the gap between the window sill and the frame with limited expanding foam. Foam holds the window securely in place and is water and mold resistant.
Secure the window well to the foundation with 1/4 inch Tap-Cons and washers. Slope the soil away from the window for the first foot, then dig out a hole about 1 1/2 to 2 feet deep. This will direct any water that should enter the well to flow away from the foundation and dissipate into the soil. Back fill the well with pea gravel, then fill the well with gravel. Place some of the excavated soil against the foundation and the well so as to provide enough slope to encourage water drainage away from the house and window well. Install drip cap under the siding and trim out window with either maintenance free brick molding as shown here, or cedar.