Hi
It's a bit hard to say rom the info you've given It really depends on completeness and originality, Have the fixed bars been removed and repalced with spring bars? Has the external caseback engraving being polished out or altered in any way? Have you seen inside the case to check that it's the correct case reference, that the the soft iron movement cover and spacer are in place and that the movement is the correct calibre and serial number for a '53?
If all of the above check out Ok I'd estimate between £900 and £1100 depending on condition of dial and movement. However, I'm not a milwatch collector so couldn't be sure that that reflects current market values. Hope it works out Ok for you, they are cracking watches.
Cheers
Ian