Valve adjustment question

[Jon Feiber <jdf@mdv.com>]

I am adjusting the valves on my J2, and I cannot get any more than .001
clearance on the 8th (most rearward) valve.  Any thoughts or suggestions
before I (regretfully) think about tearing apart the valve train?  The rest
of the valves adjust fine.  I've noticed that the large eccentric nuts that
the rockers sit on seem to be numbered.  Are they unique in any way?

Thanks!