As was posted, go to the G503 forum,
www.g503.com, it is the best jeep-specific site on the 'net, although heavily centred around American jeeps....you'll find out more than enough info there for you.
Data plates, there is a guy in Europe that does a great set of repro plates, find out your D.O.D. and go from there.
To get your serial number there are a couple places to look. First is on the frame just inside the left (driver's side) bumper gusset, there SHOULD be a tag there stamped MBXXXXXX, which will give you your frame number. Now, that is if you actually have a Willys MB...if a Ford GPW it should be stamped on the upper side of the frame rail...easy way to tel is the front cross-member...oval is Willys (or very early Ford), while U-shaped is GPW.
Second spot is on the toeboard gusset, there should be a body number stamped on there.
Third place should be the engine serial number, if original to the jeep can give you an idea to the D.O.D.
Get those numbers and head over to the G503 forum, they have "experts" over there that can tell you with pretty good accuracy what the D.O.D. of your jeep would be, you can go from there.
Saying that, if you have NO data plates/original items (as on my jeep) there are several features you can use on the frame/drivetrain to hep date the jeep....again, the info is on the site. I was (still am) missing the data plates from my jeep, so I looked at the features my jeep had and can guesstimate a general D.O.D. for mine. Not close...but close enough....
Hope that helps,
Tim