Now we can get into a solution! Nice pics, just what we need!
I'm not certain this is the issue, but you do need to verify the vacuum path for the pcv plumbing through the throttle body/carb base gasket/intake manifold plenum and make sure it's unimpeded and the pcv "flow" can access the primary throttle bores at all times.
There were variations in the carb-base/mounting on the spread bore manifolds on the ihc stuff, at least two that I have seen though I have no samples of those here now for verification/pics. And likewise, there are several variations of both the 2v manifold and 4v manifolds used for the "squarebore" flanges (2v flange is 1/2 of a squarebore 4v flange).
Some manifolds had a pressed-in 3/8" nipple fitting for the pcv hose at the rear base of the carb mount that entered directly into the manifold plenum for the crankcase gases to be mixed with the incoming fuel/air charge and be "re-burned". Others did not and plumbed the pcv through the vacuum tree, or some other vacuum port installed in a manifold runner.
If you don't have exactly the correct base gasket between the quadra and the intake manifold, then you are blocking the route of the pcv gases into the manifold plenum. That results in crankcase pressurization and manifests itself in oil leaks through any gasket/seal interface at certain rpm/manifold vacuum levels, along with liquid oil blowout at the dipstick (pressurization of the crankcase).
Look at this pic of two oem quadras I have on the bench for build now, see the tiny bleed passage from the pcv inlet plenum to the primary throttle bores??? Those carbs must be mounted with a heat dam gasket (the thick one!) that allows plenty of flow through that area to be able to evacuate the crankcase in sufficient volume above 1500rpm/cruise vacuum.
For the quadrajet carb alone, my reference/catalog shows twenty-four distinctly different heat dam base gaskets, these are quadra-specific for quadra-specific oem intake manifolds! Same items for the thermoquad...only four distinctly different gaskets with no interchangeability with the quadra gaskets.
This same situation can arise with the squarebore intake/carb combos since the edelbrock clones of the carter afb/avs are bastards in the throttle body deign/bore spacing/pcv plumbing area. And some Holley 4v aftermarket carbs will have this issue when mounted to some ihc oem manifolds. This is why the aftermarket carbs are not considered direct replacements for oem stuff. Yes, they will mount, but it takes much knowledge of flow patterns, vacuum paths, etc. To tune the things in and allow the pcv to operate properly.
I have delt with this same issue with my personal Holley 80457 carb mounted on the rpt aluminum intake. I've plumbed the pcv several different ways. Because that manifold pattern is based upon the last gen oem egr casting for the sv motors, and Mike designed it for the performance aspect but still allow it to be an oem replacement, he did not make provisions for the pcv nipple in the rear of the plenum, thus it must be plumbed either into the carb throttle body selected, into a spacer which incorporates a pcv nipple, or a workaround port added for pcv.
I originally plumbed the pcv into the carb throttle body on my setup and that does not allow sufficient vacuum/flow to operate the pcv except at idle since it dumps only into the secondaries which are closed most of the time in cruise mode!! That was not the only issue I had with pcv in general due to the air cleaner setup and some other plumbing I did originally, but over time I've worked all that out though it's not as neat as what I had in the beginning!
The quickfix for your rig right now for verification, install a tee fitting into the manifold runner that feeds your vacuum brake booster and run the pcv hose right there! I've been running that way now for about 5k miles and that did it!
And like I remind folks all the time around here..."they are not all the same"...especially when dealing with the huge variety of carburetion we find either po-induced on this stuff or the incorrect apps obtained off the I-net and egay!
