As promised here are dimensions on the lower / aft portion of the 2 piece sliding hatch.
length = 24"
width = 20 1/8"
This hatch is 7/8" thick at the edge but only 1/2" thick elsewhere.
-I see no reason why this hatch could not be 7/8" thick all over as it slides on the edge not the thinner center area.
-There is a piece of plexiglass mounted to the under side of the hatch 2" forward of the aft edge. This piece aligns with the top of the sliding cabin door and fills the area between the hatch and the door when both are closed.
-There is also a strip about 1/2" square mounted to the top of the hatch to keep the lower hatch from sliding to far under the upper hatch.
Here's a picture I added to my gallery that may help.
http://www.wellcraftv20.com/gallery/...op_up_pics_007