There is no such thing AFAIK.
There are however Dart heads; and there are also World Products Sportsman II heads. www.dartheads.com www.worldcastings.com
Which one are they?
268 @ .600" isn't particularly outstanding. No slouch, but certainly not world-beating.
As far as what they're worth and whether that's a good deal, I have no clue; not knowing the exchange rate today. It would depend on WHAT springs are on them, and WHAT rockers they are, and so on. "New", "stock", etc. are not adequate descriptions. It would also depend on what you're planning on doing with them. If they have "new" Comp 981 springs and you're planning on running a solid roller cam, then they're not much good to you. On the other hand, if they're Manley Nextek springs and you're planning on running a Performer RPM hydraulic cam, they're not much good either.
In other words, details matter. ALL OF THEM.