Hi Trans
Sorry to pour a bit of cold water on things, but from what I have read above and from your photos, I'm not convinced that it is a Supreme. My feeling is that the numbers you have quoted are probably just lug casting numbers. As 33d6 mentions, the frame number should be stamped just below the saddle on the flywheel side of the bike. If it is an Ambassador, (in 1951/52) it should start with a letter and then be followed by seven or eight numbers. I agree that there are quite a few similarities between your bike and a 1951 Supreme, but equally there are a few key differences, the main one for me, being the rear plungers which are ever-so-slightly different in design to the Ambassador versions. Also, your seat post looks to come up above the sloping line of the rear frame tubes, as though it has provision to fit a seat post. Ambassador frames of this period did not have this and featured a lug which just curved around to join the tubes behind and above the engine. I agree that the headlamp bracket does share a similarity with those used on the 1950 Ambassador Series V, but your forks are not those as featured on that model.
See if you can find that frame number - that will confirm things, in terms of it being an Ambassador or not. Happy to send you further information.
Regards
Michael
PS - my email address has changed and is now ambassadorguide@gmail.com