Vaccuum Advance on '71 Scout

[MikeIIDC@domain.elided]

Well, before I go to the auto parts store, let me ask this:
With my "Running Better but Still a Little Rough" '71 800 Scout, I have
it running well enough to go down the road, pick up enough speed, and it
hasn't fallen apart on me yet.  I am overall very happy with this
situation.  However, I am trying to further fine tune it, as it has what
I now officially call a "hiccup" when I'm driving down the road.  It
runs fine, but makes little, very gentle and muffled pops when I go down
the road.  Since I've driven it so little, and it has holes in the floor
and no carpet, and very little interior fabric to deaden sound, I am
still getting adjusted to the acoustics of this particular vehicle.
they do not sound to me like "pings," and seem to come in a little
cluster of two or three every few seconds.  I have not use a timing
light on the thing, but the timing was set with the tune-up-done by a
buddy-when I first got it, and I have checked it "by ear" and it seems
to be pretty optimally set.  I checked the points gap, and the tune-up
is very recent.
I went out this morning to try to check vacuum advance.  First I tried
spraying "starter" fluid around the base of the carb and all hose
fittings and junctions to listen for acceleration.  Nothing here.  I
then hooked up the vaccuum pump to a "t" fitting that has multiple
branches coming out of the distributor.  It has a branch to the
"charcoal canister," one to the distributor, one to the carb, and one to
a plug sticking out of the top of the rear of the intake manifold.  When
I disconnect the carb hose from this conglomeration and try to build up
some vacuum, nothing holds.  I can hear the hiss of the carb hose, but
the pump builds up no pressure no matter how hard or quickly I pump.
There is also no reaction in terms of RPMs.  If I reattach this and hook
my vacuum pump directly into the spout from the distributor, it holds
pressure up to about 20-25 when I quite pumping, but I get no reaction
from the engine here either.  I was under the belief that this vaccuum
advance would trigger an increase in RPM's.  Is this true?  If so, does
this automatically mean I need a new distributor?  what about the other
lines not holding vaccum?  Should they?  Should I change the hoses
first, then see if it runs better, or does the lack of vaccuum effect on
the distributor mean that I definitely need a new dist regardless?  And
does the lack of vacuum in the others mean I definitely need new hoses,
or is there a possibility of a bad component?  Something in the canister
leaking, etc?  If the dist is bad, how much interchange did IH use on
these?  For testing purposes, could I pull the one out of my '68 345 and
try it out?
Any other input on this?
Thanks in Advance, once again!

Michael