BP, I believe when both arms are installed in those direct mount bosses, and the stradle cable is in place, they will look much like the original MAFAC center-pull brakes. Several Shimano and some one off smaller mfgrs. are using direst mount for both side pull and center pull brake sets. But, you are close in seeing the resemblance to some U-Brake models, too.
Are you using the TRP blended hydraulic and cable brakes on your low rider?
Bill
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Semper Fi, USMC, 1975-1977
I Can Do All Things Through Him, Who Gives Me Strength. Philippians 4:13