So... i had a productive day, i made a short video, the thing works.
I even made it a talkie and recorded it in color!
https://www.youtube.com/watch?v=fAF2qS8L6hI
And now for a bit of good news, bad news.
It seems either i did my math wrong or the circuit is misbehaving a bit, i poked and prodded it a bit with the scope and it seems to be working like it should.
And since i can barely count to five i will go with, my math was wrong.
The max current is around 160mA when running 4 LEDs in series, otherwise the regulator gets a bit toasty.
I say four since these LEDs have 2 dies in each package.
That either means i could stay with 2 LEDs and get more efficiency or just use one LED and run that one at 250mA, that should work but would be less efficient.
It should be a difference of about 15 Lumen/Watt, that is not much.
It makes more sense to just use one LED, that would mean, i only get 169 Lumen out of this thing, still enough for me but short of my target.
That was the bad news, now for the good news, all that means that the cooling is not as problematic anymore, two PCBs should do it just fine.
But i will test that.