Hi guys...caught my eye while lurking and thought I'd stop by and say hi.
The PHB does change the RRCH drastically and it is definitely noticeable, a big improvement in feel and response. Is it the right way, of course not, neither is adding one to a leaf application but the early Mustang guys have been doing since the days of Mark Donohue and the Javelin/Camaro/Mustang wars. Bottom line is it works but there are better options. The chance of the UCA's conflicting with the PHB and creating a mechanical bind issue are virtually non-existent.
If you are serious, look into putting a 3-link together.