Seat Belt Retractor

Hello, installing seat belts with shoulder restraint in the Fast Back 68 Barracuda. This ‘68 was built in Oct of ‘67. Had the roof brackets, but not the mounting nut, I have that resolved. My question is where is the seatbelt retractor mounted? I am using a set of belts from Westco. They provided no install instructions. I am no after a 100% OE install, but would like to know how it was set up originally, realizing that in ‘68 maybe they did not have retractors.

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