Hi Geronimo, was cool talking to ya while I was up on a mountain today- I'm sitting on a log about 300 feet from a big cell tower, drinking from a canteen and my phone rings!
Anyhow thanks for the pics this helps heaps. OK first your Grooves look good far as I can see. Large bit, full width, next time the carb is loose take the large bit and check that the bit cutter bottoms out in both Grooves all the way through, known as checking for full depth of cut. The cutter ball should bottom out so the shaft taper behind the cutter is touching the bore wall. In your case there IS no bore left at bottom of Grooves, just try to judge it, if it isnt full depth you can retouch it, be careful not to over-do it.
Next thing I see- the thick fiber carb base gasket/spacer, is it pliable or hard/dry? IF dried out it can leak vacuum. The Edelbrock Performer intakes usually are made such that the opening at top goes wider to accept the stock Quadrajet carb secondaries. A flat spacer like you used can cover the wider secondary section of the plenum opening. Edelbrock makes a flat thin metal adapter plate to be used in applications like yours here. You use a thin carb. base gasket, open style, then the metal adapter plate, then another thin open carb base gasket, stacked bottom-up. Go to any parts store look for a Holley 4 bbl square bore open center base gasket, that's the style to use, just put the Edelbrock metal plate between 2 of these gaskets. This ensures a good carb to intake manifold seal. You can put additional spacers atop this stack if wanted. I have found those thick fiber carb base gaskets like yours to be unreliable, they can leak vacuum, and don't seal that well.Those compression limiter rings at the bolt holes exacerbate the issue. Look on Summit Racing's online site you will see the Edelbrock adapter plate, anf mayber copies of it it's not expensive, that's the only way I will setup an Edelbrock/AFB carb on the Performer intakes.
Next of course is the issue of the PCV/ crankase breather, and doing the PCV re-route to it. I'm not absolutely certain, but the Driver side valve cover might have originally had the breather tube that went to the stock air cleaner. Having 2 PCv valves w/ no crankcase ventilation breather provision is a no-no. See if the driver side grommet is a larger diameter than the pass. side. The larger diameter grommet would be the breather side. Check the air cleaner base plate, seeif there is a provision to add any fittings to it, many aftermarket ones have this. What is needed to do a "correct" PCV re-route is: New pliable grommets for both valve cover holes, a 90 degree fitting to fit the driver side grommet hole ( Look in a "HELP" section at parts store, or boneyard) or it might have had a metal pipe w/ the 90 deg. bend in it, look at other Chevy's. A knockout plug or just a drilled hole to fit the aircleaner base, to take a fiitting the same size ID as the hose that will come from the driver side valve cover. There's supposed to be a hose, that connects from inboard of the air filter element, to direct fresh filtered air to the fitting on the Driver side valve cover. This is the MAke-up air side of the Crankcase Ventilation system. The PCV on the other valve cover, goes to the carb base of course (Capt. Obvious here). The manifold vacuum sucks the crankcase gasses thru the PCV Valve to the carb base, the Breather side lets in the fresh Make Up air, see?
With all that said, get a breather hose done from the driver valve cover to air cleaner base, opening inboard of the filter. THEN---Cap the PCV tube at carb base, run PCV valve hose over and tee it into the new Breather hose. That's It.
I've never seen an engine w/ 2 PCV valves!
IT is possible as you say that some tuning was done before to compensate for this unusual setup. Somebody just took a shortcut w/ the crankcase vent. system. I'm not surprised I've seen lots of stuff like this before. The details on setting up aftermarket carbs, hoses, vacuum lines etc. etc., are sniggly. I dont think it's going to be possible to troubleshoot this engine until the carb base gasket and PCV/Breather stuff is right.
And I notice the nice MSD upgrades, very nice! (IGnition Freak here!)
As well as the Magnetic stuff. LAstly, Gernimo, maybe while you re-do the carb base setup and the carb is off, get the Edelbrock torque specs and sequence info- and check the intake bolt torque's. The Edelbrock torque values will prob. be different from Factory Specs, pay attention here. But Don't loosen the bolts all the way, unless you partially drain the coolant dont want coolant leaking at manifold/ head junction. IT's a goood idea to do an intake man. re-torque, I proved it again earlier this summer on a Lincoln w/a Ford 460, original, 40 yrs old.
Out for now, thanks for the posts and great pics, Geronimo!
Tracy G