I'm about to replace the retractable seat belts in my '78 with a NOS set I acquired. I haven't taken the panel covers off yet, but looking at the mechanism it looks to be a pretty straightforward r & r. If there's any secret to it or pitfalls I need to be aware of, I'd appreciate the advice. Thanks.

Don't mix up the bolts, they all look the same, but there are different lengths. You might want to start soaking those 2 lower bolts next to the doors with PB Blaster or Silicroil a day or 2 before you intend to do the actual work.