Your dad was a wise man–just like mine!
I did a bit more mental engineering. I believe I can rework the PVC to add a section of pipe on the filter outlet that will allow both the 12" run and fit the IntelliPH injector prior to the IC40. I'll cut the pipe at the filter outlet then put in a 6" length of pipe. Then add a T for the injector (about 4" long). Out of that I can put in the 90º and 45º couplings shown in the pics going into the IC40. To rotate everything about 12" away from the filter, I'll cut the PVC after the IC40 where it turns back down and glue it into its new place with another coupling. The only piece that I have to sacrifice of the current setup is the Pentair filter outlet union coupling–everything else can be reused as is. My estimate of cost is <$5 for the PVC fittings. However, the Pentair coupling is a proprietary part–you can only buy them in pairs and they cost $55!