Hi Mark, thanks for the reply. It looks like there were at least two styles of Eastman 2D extension rail. One with a "slotted key" as well as a "bump and groove" connection at the rail ends while the other uses a screwed in key and two rods to align/connect the rails. I have the version which uses the screw and two rods. I believe this is what the compatible rail would look like
https://www.worthpoint.com/worthopedia/eastman-kodak-2d-8x10-camera-rear-534532919.
Dimensions of my rail at the end are around 1 1/4 inch by 8 1/2 inch.