It's probably just a loose or poor connection at the switch(es). As Meteor said, pull the door switches up and inspect the connector sockets and pins. Straighten any bent pins or contacts and clean any corrosion or grime. If everything worked before, then this should get them working again.
That makes sense because at that time GM was limiting the A-Body cars to 400 CID maximum (well, 401 for Buick).
The following year brought the Q-Jet and ended multiple carbs for BOP. (Of course, Corvette still managed to get the 3x2 427.)
Yes - I've done that too. The key is to go slow and pay attention to the new pattern that appears with the first few file passes. That will identify the high and low spots. Work the low spots from behind with gentle hammer/dolly raps. Tap the high spots on the face with the hammer. Once you get close, you can carefully run the file across the face to even the surface before switching to the wet/dry paper with a sanding block.
I have a LR molding from my '67 that I replaced with another that was in better shape. The one I removed has a couple of flat spots, but I haven't yet gotten around to straightening it yet since it's now an 'extra'...
As Larry said, I hope whoever ends up with it respects the originality and performs a 'sympathetic restoration'. If it were mine I would first make it a reliable driver and then deal with cosmetic items by repairing what can be saved and only replacing items that can't take any additional wear without disintegrating. From what I see in the pictures, I'd try to salvage and preserve the existing paint.
Are you talking about the small pin perpendicular to the kingpin that intersects the kingpin bore in the knuckle and holds the kingpin in place? I think it is item "AG" in the figure...
This is the currently available GM additive:
https://www.amazon.com/ACDelco-10-4003-Limited-Lubricant-Additive/dp/B000QGMXSU/ref=asc_df_B000QGMXSU?tag=bngsmtphsnus-20&linkCode=df0&hvadid=80127027724173&hvnetw=s&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=&hvtargid=pla-4583726553782536&psc=1
I would ask that you read the book again, as what you said above is exactly the opposite of my experience. I had chattering on a 1977 Buick until I changed the differential oil and included the GM limited-slip additive. It usually takes some amount of driving (e.g., 20 ~ 50 miles) for the additive to fully treat the clutches.
Maybe the result of a prior accident (albeit minor)? Possibly a hard pothole hit? Or possibly caused by improper sling towing at some time in the past? I'm just glad that it wasn't the steering box!
It's hard to tell from the photo, but if the wheel opening molding is just flattened a bit it may be able to be straightened. I have done that before myself using a hammer and different tools to bend the stainless back into shape. Once the shape gets close it may require making some wooden dollies to get just the shape you want. Once the dent is removed then bodywork the outside surface with ever finer sandpaper. Final pass with some 1500 wet/dry paper and then polish with a cotton wheel on a bench grinder. Many other '60s cars used anodized aluminum moldings which generally can't be repaired, but the stainless steel used on the Riviera at least allows for the repair option.
Good find! There must have been a shiny spot on the rod where the tie rod end was getting caught. Hopefully after the alignment the steering wheel will be set straight and the tie rod adjusters should show roughly the same number of exposed threads.
Yeah, I see that now - I thought the picture was looking from the back, but the Q-Jet shows otherwise. Anyway, my point was the difference in complexity that ~15 years of EPA regulations made on vacuum engine controls...