The date at 6 is case ref. 2627 and the date at 3 is case ref. 2849. The dial you are referring to came only in 14k cases for either reference and these dials were not exclusive to these models. In fact the vast majority of these watches were in stainless steel or gold cap and featured the "regular" dome seamaster dials. The dial you are referring to - solid 18k gold piepan dial with the "scalloped edges" is a very uncommon variant of either case reference. Even the de luxe piepan dial version in 18k gold with the "plain" edge is relatively more common. I think the specific model you are referring to - the "grand luxe" style seamaster dial - less than 10 examples have surfaced in either date at 3 or date at 6 versions at least as long as I have been deeply involved in vintage omegas which is to say the past 5 years or so.

Now don't ask me why omega placed these magnificent 18k gold seamaster piepan dials in 14k gold cases instead of 18k cases but all the examples that I know of that have surfaced so far have this configuration.

 

The date at six ones also all had wrong length hands from new for some reason

 

You won't find a Seamaster Piepan with the help of your AD, they wouldn't even know they existed. You /might/ get lucky and have an AD able to find a Constellation deluxe/grand luxe but it will likely be a polished up example with a price tag double that of its real value.