Thank you for pointing out the information that I missed posting earlier.
I don't have the camera yet however, the previous owner told me that the dimensions of the rear "standard" are 10 x 10 inches.
This particular Conley model was made in a variety of sizes, the two largest being the 8 x 10 and the full plate 6 1/2 x 8 1/2. I suspect that this means the camera is the full plate version.
It has been modified for 5 x 7 which I will keep but I also wish to make backs for full plate and 4 x 5.
I will post more exact information and perhaps a couple of quick picks as soon as I receive the real thing.