Emtek 5302 Modern Rectangular Single Point Lock

Q: I have an antique horse stable door used as a font door. It is 2 1/4" thick. There is a mortise lockset but it has caused issues because the mortise box wasn't centered when installed so the exterior cylinder and the interior cylinder are different lengths. I want to transition to a tubular entry set and fill in the space where the mortise box was but all of the tubular entry sets I find are 2 3/8" backset and I have a 2 1/2" backset. I have further restrictions becuase I can't have an exterior or interior plate that is wider than 2 1/2" or longer than 9". I want knobs not levers. How, if possible, can I make this work. Thanks