[ QUOTE ] there is actually no keystone in the reference... weird [/ QUOTE ] As Tumerboy alludes to, there is ALWAYS a central brick at the top of the arch, and not a crack between two bricks. That's the keystone. Wether or not it looks different from the other bricks is gravy.
The arch-bricks should be angled/shaved/beveled, so they sit flush with each other... this is why they look like a veneer and don't support weight. I really like it though. Good start.
the archway bricks seem kind of soft & cartoony to me and they don't look like they really support anything, but are more of a veneer. What's the stuff behind them & to the right on the first picture? I'd tighten up the gaps & overhang significantly.
http://www.flickr.com/photos/darwinist/21542160/ Notice that there are waterstains, but they are spread all along the upper edge. Having 2 in very specific spots makes me look for a reason for them to be there. Having them along the whole top edge means that it doesn't need a specific purpose.…