I finally tapped my vacuum system for a gauge. What I did was take a 3/16" plastic T, the tap side I put on a piece of 1/8" ID hose, slide the 1/8" od hard nylon line from the gauge in to it and used heat shrink tubing to seal it tight.

For the T to stock male fitting, I just a coupler I found on my parts engine, but a peice of 3/16" hose should do well, then the stock female fitting slid right on to the T.

Very nice fit and finish.