Thanks, guys. Yep, putting the four barrel on the engine showed that the motor is ok, it is the fuel delivery system that was messed up. Now I have a baseline to start from.
What drives me nuts is, by blocking off the two end carbs and getting them totally out of the picture, basically I have just turned this engine into a two barrel motor. That is about as basic and simple as you can get. To still have issues shows that the vacuum leak is either coming from the intake to head area, or the carb itself.
Now that I have successfully sealed the four barrel intake to the heads, that tells me that there is no misalignment there, the heads must be true and the intake seals to those heads just fine. Now I have to spend the same amount of time and carefully seat the tripower intake to the heads, and then play around with the center carb to make sure it is doing it's job correctly.
I honestly think my center carb was the issue, with the back plate missing and the goofy job the rebuilder did on plugging the hole back there.
Today I worked on cleaning up the sheetmetal parts for the bed. I cleaned the tailgate of some of the little rust spots that it got from handling it, and also cleaned the front plate that makes up the front of the bed, and also the 4 stake pockets. I DA'd everything with 80 grit and then hit it all with a scotchbrite pad. They are all now very clean and one more wipe down will make them ready to prime and then paint.
That will leave only the two side panels and the louvered top piece. So, by the time the powercoater is done, I should be in good shape to assemble the bed for the final time.