I have an alternative based on some advice here, as usual.
OK, everyone has their favorite ways and means. For me, I did not want to carve up my vintage tunnel. Don't forget, fitting that 3/16 "bit" into the adjusting arm on the passenger side also requires room. What I did was drill a small hole in the tunnel on that side so that I could move the carpet aside and slide a bit in there for the adjustment. Then, on the driver's side I took some advice from Randall (anyone done that?) and replaced the bolt on the pinch fitting on the operating shaft (solenoid side) with an Allen head screw so that I could tighten and adjust from underneath. So far, all has been great, and I adjusted lying on my back and with the tunnel left on.