I did a setup that I adapted from a '92 Dodge van. Posted a raft of pics a couple of years ago. Might still be here somewhere.

Anyhoo, retractor and frame rail end of lap belt portion both bolt to frame rail anchor point. It has a dogbone, like an earlier poster mentioned, that attaches to the roof rail anchor point, which drops and moves forward the shoulder portion of the belt so that it lays across the shoulder/chest properly. The dogbone also allows the belt to hinge out of the way nicely for entry to the rear seat. Webbing and buckles are black, like originals. Car is a '72 RR.

This shot is early in the adaptation. Trimmed the plate down more and redrilled it to hide it under the retractor cover better.