That diamond is not the cam timing mark that I am familiar with. All, no exception, cam sprockets had a triangle on the edge of the sprocket. That triangle was aligned with the mark on the front of the head. The mark on the belt guide is not the one to use as far as I know.
Take a bit of cleaner, wet a shop rag, and wipe the front edge of the sprocket. If you have removed the sprocket, could it have been installed with the mark at the back? I don't remember if the design allowed for install thataway or if the belt would have been way out of position, so offer it as one explanation if you can't find the triangle.
I think the diamond is the mark on the auxiliary shaft, but don't be the farm on that one.
If you can see the sprocket keyway, I think it is supposed to be at noon also.
The cam lobes should both have their followers on the 'heel' of the lobe, and the exhaust valve should be about 180 from being on the lobe tip. IOW, the piston should go down from TDC to BDC, the exhaust valve open about THEN, and then the piston come back to TDC, pushing exhaust out through the exhaust valve. THEN the intake valve should be opened as the piston starts downward... fill with fuel:air, then close ~BDC, compress, back up to TDC FIRE!!!! and onwards. You can tell by looking what the lobes are doing/going to do to the valves.
tom