[chuckstinn]

You said you are using the original springs and brackets that you removed from the car and the brackets are 3/4" high as opposed to 5/8". I’m not sure about the ¾” bars.
My vender parts catalogs (Bratton’s, Snyder’s, etc.) say the rear spring clip bars for the 10 leaf springs are 5/8”. I wonder if you replace the 3/4” bars with 5/8” bars if the extra 1/8” would give you the needed space to tighten the castle nuts.