Yep, it was a vacuum hose - the one below the S/C snorkel (since when I replaced fittings and the tee fitting here was not available, I used a universal part. Its size is a bit larger than the port at the manifold which lead to slightly oversized vacuum tubing. I recall knowing it wasn't the tightest fit, so I found some other tubing and used a spring-ring. It appears to be good, and I might even find some intermittent misfires go away. Whew.

Thanks for reading, FordMan77.