So let's dig in!
Here are some of my cal. 30 watches. I am sure they all have original dials. I have focused on the Omega script, which has raised some doubt in the OP's watch. But I have not chosen only Dennison's cased Omegas, as it is not a real factor as far as dials are concerned. I apologize for the poors pics: I have use my phone and sometimes a x15 eyeglass...
Let's start with two 285, one with a Dennison 9k case and one with a French 18k case. Both have a pointy A, so not relevant for our dial check, but still interesting for the record:
Now a 283 with a 80 microns Swiss made case (for the French market).
Next a 284, with a 18K French made case. We are getting closer as the sherifs are more curved (with the ends rising a little bit) as in the OP's watch.
We end with a 283 with a 18K Dennison case (I have removed the bezel for the pics). I would say we are very close to the OP's dial. The Omega scripts look almost the same: same flat A, same sherifs. And the rest of the dial is very similar as well - except from the cross hair and the numerals of course.
As I said in my first reply in this thread, one would expect watches with 285 to have rather a pointy A. But there are no general rules here, and I still think the OP's dial is genuine. Again, other pics (if possible without the glass) would help to make a definive judgement.
Edit: sorry for the two last pics: error of manipulation, and I cannot delate them without delating other pics...