On early to mid-1960 225's, the vacuum advance would connect to a port
on the base of the carburator. When emission control equipment started
to arrive later in the decade, that most likely changed.

-Kirk Matheson

I think it comes off a small port on the intake manifold.  If it's not
there, maybe it fell off and is causing a (small) vacuum leak which
will affect performance.

There are a few things you should measure on this engine if you have
the inclination.

1) If the engine really did come from a '68 truck, then it probably
  does not have hydraulic tappets - which means the rocker arms
  are manually adjusted (valve lift) while running (interesting
  experience).

2) set the idle RPM to 550 and connect a vacuum gage to the
  intake manifold.  Leave the vacuum line connected to the
  distributor.  Rotate the distributor so that the vacuum
  reads the highest value (which is dependent on your altitude
  but at sea level if the engine has good valves/seals/rings
  you should be able to pull 20 to 23 inches of mercury.  Once
  you've found the max setting, lock down the distributor.
  (this setting may not give you the best emissions but it
  should give you the best milage and performance).

3) If you're so inclined, get new plugs and points/condenser
  and set the distributor up properly (dwell).  Gap the plugs
  before you put them in.  Maybe new primary coil and wires,
  fuel and air filter.  If you do any of this, do it before
  performing step 2.

4) If you're really keen, you can get a carb kit and take the
  Carter apart.  Change needle valve, check the floats, replace
  the gaskets, etc.  Note that the upper and lower surface of
  the air horn are prone to warping and don't always seal
  nicely.  I've sanded mine down to insure a good seal.  Be
  carefull that you don't turn down the long screws too
  tight or you'll warp the air horn.  If your float and needle
  assembly isin't set correctly you'll have gasoline gushing
  all over the engine so be ready to shut it down the first
  time.

5) Get a compression guage and check the cylinder compression
  values.  I think that you should get values of 100 psi
  (+/- 20) - the higher the better, and the more even or
  similar the better (although I wouldn't be happy with all
  6 giving 80 psi vs 120 psi.

6) perform a leak-down test (crank the engine so that the
  valves for each cylinder are closed and then with
  compressed air give the cylinder a charge and then
  watch how quickly the charge bleeds away.  This will give
  you some indication of the health of the valve seals,
  rings, valve seats, etc.  

Oh man looking back (15 years ago) boy did I spend too much time
working on my slant-6.  Was nice when I had the time...

The vacuum advance hose gets connected to the one and only
appropriate-diameter hose nipple on the passenger side of the carb. This
is ported vacuum.

Head over to www.slantsix.org for quality advice on this car.

DS

"" wrote:

Base of the carb. You’ll know which one it is by pulling off the plug
and checking for vacuum at idle. If there is no vacuum at idle gently
hit the gas and see if vacuum presents itself. If so thats the
baby...... Chrysler used timed advance..