Rich,
Not to beat a dead horse, but did you locate the MAP sensor vacuum line at the rear of the plenum and check to see it is still on the plenum port and not filled with oil?
Sorry, not trying to be a wise guy...
It is important that the MAP is getting a vacuum signal. That hose is the first casualty if the motor backfires at start up. It can also get loose with age and come off very easily if you were poking around back there...like working on the bottom PCV hose.
I'll PM you my digits just in case you need moral support!
Tom