No ported vacuum???

[mrk3cobra]

Not sure if there is some overlap on the cam.

I read that you can pressurize the intake to try and find leaks, when I pressurize the intake it will not hold 3psi. I hook up a compressor shoot in 3psi and it drops to 0 as soon as I turn off the compressor.

[omaha]

you should back off the rockers. Invariably, there has got to be at least one exhaust valve that is open.
I have never heard of pressurizing the intake to check for leaks though. It woud seem that it would be difficult to keep  the pressure from escaping out of the various vacuum ports. Even withh caps on them it would seem that the pressure would just "blow" them  off.
          You want to hear a crazy one?, I did this back in the old days. I taped up the opening of the carb throut with tape except for a straw sticking up through. Then I blocked open the throttle linkage just a bit. Then light a cigarette and blew some smoke through the straw. The smoke will find the vacuum leak is what I was told by an old timer mechanic (back in 1983).   Guess what, it actually worked. The cigarette smoke magically appeared coming from a crack in my vacuum advance canister (on my '67 GTO). I thought it was great but looking back maybe it was kinda dangerous.

[chewy]

      Perhaps this will shed some light on your mysterious lack of ported vacuum. My  Canadian built  1986 Cutlass  came from the factory  with an LG4 305 chevy that has the m4med quadrajet (probably the same carb as in your truck). Oddly enough, this carb does NOT have ported vacuum. The "ported" vacuum source on the passenger side front is actually an EGR signal ("J" on Carburetor), not a true ported source and is therefore not suitable for ported spark advance. The port on the front of the driver's side which is typically ported is in fact full manifold vacuum ("H" on Carburetor).  The signal that gets to the distributor can comes from a tvs that is connected to the EGR "J" and Manifold "H" vacuum sources.
      In addition, the M4med has a dual capacity accelerator pump which varies accelerator pump shot with temperature. Strange carburetor indeed!
Jason