Mounting Electronic Unloader Valve

I have 2 vertical compressors that I would like to link together using the SAM Compressor Controllers. The one thing I want to be sure of is the knowing where the Unloader valve should be mounted. I bought the valve recommended in a prior article, but I am not sure where it should be installed on the compressor. I have identified the unloader line, but am unsure where the vent valve should go along that line. See the images of my two compressors below.