How did this last Compression test turn out? From some of your other descriptions it dose sound like you have most of your tune up settings just about right the only thing that I can think of besides the possibility of the Vacuum leaks. Is that maybe some of your the carb settings could use some tweaking (see below for some tune up specs I use to get them running).
Over the years I found this is best order and quickest way to dial in a basic running tuneup and some of the specs to use to get them into the ball park! Updated Now that I know most of your combo of parts
1. Set your Spark Plug Gaps for DSII (.044 to .045) and then install the plugs.
2. Next set your Base Timing with Vacuum to Distribitor disconnected and 12 to 16 degrees BTDC. i.e. Taking into consideration the Air Temps and Elevation, etc. in your area I personally like to use a Ported Vacuum Sorce if possible for any street type car IMOP this gives better drivability and economy. Manifold Vacuum will also work though it takes a little different level of tuning.
3. Now you will need to verify the carbs float level setting is correct for a Holley you can remove the fuel bowl plug to check it (if you have a glass type plug then there is no need to remove) the wet fuel level should be just at the bottom of the hole with the engine idling.
4. Holley 350 CFM 2V carb the Power Valve to install is yet to be determined. Example would be 5.5 Hg if your Idle Vacuum reading stays at 11Hg with the parking brake set and the Auto trans in drive.
5. Next set your carb mixture to the lean best idle, the starting setting after a carb rebuild is usually 1 1/2 turns out. With a tach hooked up and engine warmed up to normal operating temp. Turn the mixture screw or screws each in until idle speed drops slightly then turn screw out until you reach highest idle RPM then turn the screw back in 1/4 turn (Leaning it) this is your lean best idle setting.
6. Last set the Curb Idle RPM (500 to 600 in Drive with parking brake set). This setting is for a mostly stock engine combo, you may need to raise it some depending on your location etc. IE with car in gear punching it and taking off there shouldn't be any stumbling.
7. If the carb still has all the working choke parts then it now needs to be set also. Auto or Elec. choke is set about 2 index marks past center Index Mark to the Rich side. And with the fast idle screw set on the fast idle cam index Mark (>) you will want to adjust screw so it's from 1200 to 1500 RPM or just a high enough RPM so that the car will drive without stalling. When warmed up choke should release the fast idle cam and choke blade should be fully open. Recheck this setup after the engine is cold again to see if it resets the Fast Idle cam and the choke blade closes.
For the best results I usually repeat steps 5, & 6 just to verify that the carb settings are right. You know the tune is good if the car starts when warmed up without touching the gas pedal! This should give you a good basic tune to adjust from and fine tune it since every engine can like a slightly different tune. You can then try molding the tune (do only one thing at a time though) until you find the sweet spot that your engine likes. Remember if you change base timing then you will also need to reset the carbs Idle Mixture and reset the Curb Idle again. If you decide to use some sealer on your intake gaskets you can try something like the Permatex Non Hardening type, I don't use any of the Silicone types around fuel.
By the way I would also swap my good 1981 200 Mustang head for that 2V setup and even do all the install and tune, :rolflmao:. Just kidding you Rambo I think your real close now to getting it right and like you said it's going to be something simple. Good luck in your tuning!