Sometimes the easier way is better: so, a
complete change of plan! One piece PVC deflector that connects to only the two
inside headrest posts. About $20 for PVC, fiberglass screen, glue and paint. I hope to have it finished and test drive it Saturday. More photos then, and maybe parts list if there is any interest. DIY only, not planning to Mfg. or sell.
Test drive went great!

The secret is to cut 4 - 1/4 - 3/8" wide strips from vacuum or other rubber hose & cut diameter to fit in each end of both "T"s that connect to the headrest rods. This stops rattles & vibration & creates a firmer, more vertical fit. Glue in with contact cement.

More info and parts list in the photo album linked BELOW.