16V Timing question... again

[rhock99 at epix.net (Ryan H)]

OK, this is weird.  When I line the cam sprocket up to the top of the head (or valve cover), the chain gear mark is below the head by about .5 tooth.  Could TT have tapped the chain wheel on slightly off, or is this a precise process with a no-tolerance key notch?  Or could my cam sprocket have gone on slightly off?  It seemed to fit good.
I have no idea what's going on with my timing.  I only have one notch in my flywheel.  When the cams are TDC (according to the chain wheels), I put this notch in the center of the hole (where the bellhousing mark is supposed to be which I don't have either).  I think that is off by 6 degrees, but if my chainwheels are off anyway, the whole process is shot to hell.  Damn timing.