Finally got this done.
Thought I'd share a few particulars for future visitors
who stumble upon this posting.
The two oblong holes with the gromets are not for
adjusting the adjusters. And, as I first suspected,
there's only one adjuster.
I discovered a third hole in the back plate just forward
of the wheel Cylinder and down a bit. No chance to use
a flashlight on it since it's immediate background is the leaf
spring. But, it's that hole, closer to the top center which
is used for adjuster adjustment.
The adjuster wheel is left-handed threaded (at least on the
passenger side) so a top down motion of the away end of
a flat blade screwdriver tightens (spreads) the shoes. To
loosen them, the screwdriver motion would be down to up
at the away end.
As for the two oblong holes, these can potentially come
in handy for those, like me, who have a stuck drum.
The hole spans both a portion of the brake shoe and the
inner edge of the drum. A rod placed onto the drum rim
there, then, could be used for driving the drum off from
behind the plate.
It's also useful for checking to see if the brake shoes are
loose enough to not prevent drum removable (at least for
that reason). Pushing a rod through that slot toward the center
side will engage the shoe. Pushing on it will provide some
lateral drift of the shoe indicating it loose enough from the drum.
Also note for the C1500 V-6 4.3L short/wide bed truck, the wheel
cylinder is the 1-1/8" version since, apparently, there are several
sizes and no model association to determine which goes with
what model, at least at O'Reily's.
FWIW, today a wheel cylinder cost me about $12 and was
a complete unit, not just a rebuild kit. Just bolt it on, bleed
it and you're done.
