Vacuum/boost signal

The plenum wall at front or rear is likely pretty thin, but if you are careful you should be able to tap a 1/8 pipe thread in there. Due to blower overhang you may need to connect the hose/ fitting before the blower is installed etc.

If you are not comfortable with the thin material, and this looks like a new? piece, you could have a welder tig an aluminum boss in the rear wall to add strength, then drill and tap that