You guys have me a bit confused. I've always understood the rear sway bars for A-body & B-Body to be the same, but the shims are required when using it on a B-body.
LT1Caddy, what car are you putting it on? You've asked about a 66 Beaumont/Chevelle.
And contrary to what people may say, the A bodies sometimes required shims too. I've pulled bars off a number of wrecking yard A bodies and I don't think I've ever had one without shims but the B bodies need more shimming than the A body.
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars
I just winged it all on the 65. Put a Hotchkiss on the 67.
The top illustration I linked has all the dimensions of the washers (3 in the GM drawing), special spacers (4), round or square, you choose, long flat reinforcements (5) and the inner pipe special spacer (7).
Drill the 3 holes in each arm exactly as the drawing shows, fit all the washers, spacers, reinforcements, bolts and nuts as shown and it will all come together with little or no binding.
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65 Laurentian post, 67 Grande Parisienne 4 door HT.