I would say they are 1/4 size large. I base this on the fact that the Alden Barrie last is widely considered to be 1/2 size large and the Marlow's fit a bit tighter than the Barrie. That said, many people size down 1/2 and are fine.
I am also not thoroughly convinced that the Marlow wingtip is actually on the normal 325 last.
I don't know why this keeps coming up. C&J has confirmed that it is the 325 last, one-half size down. So a 9D in the Marlow is an 8.5E on the 325. Straight from C&J.