Unless I have misunderstood your question but the Surly FAQ says they're NOT the same shell spaced differently...
The chain line of from the center outwards. Adding spacers won’t change the chain line between 130 and 135mm.
@bjf started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
Unless I have misunderstood your question but the Surly FAQ says they're NOT the same shell spaced differently...