I did it on my brother in laws truck a couple of years ago and he sold his truck last month. I don't have it on my current truck because I haven't pulled the down pipe off yet.When I get my new mount from Irate I plan on welding it in before install.
I borrowed a gauge from a friend that calibrates gauges for the military.Tapped a fitting in the oil cap,sealed it with silicone (I was very BORED that day!).at idle it showed a VERY slight vacuum,at 1500 rpm it showed almost 1in neg.The only time I got a positive reading was after running at 1800 rpm and slamming the throttle closed.Positive reading lasted about 2-3 seconds.
This is the only "turbo" vehicle I've put this on but have put the same system on 8 other N/A vehicles.ALL have worked !