Every 8" rear that I have ever seen had 2 3/4" axle tubes. A normal 9" rear has 3" tubes. The 9" with the tapered tubes used the same U-bolts as the 8". That was so the assembly line could use the same shock plates, housing ends etc. The standard Mustangs came down the line getting the 8". The higher performance version got the 9". They tapered the tubes so it would be cheaper to use existing Mustang parts.
I just went out and my shop and measured a set of U bolts. They measure 2 3/4" across the inside and are 6" long from the bottom of the U to the ends. These bolts were original to my 69 Mustang that had an 8" rear. I later changed to a 9" with the tapered tubes. Used the same bolts. It was a bolt in. I have since back-halfed the car. I narrowed the rear, but rather than cut a 9" that was sized right I sold it and got a truck rear to narrow. It has 3" tubes and would require the larger U bolts if it was used with leaf springs.
I normally like "old time" parts stores, but this is one case were the chains might have an advanatage. I know Auto Zone, Pep Boys etc all carry the new U bolts.
Later,
David Cole
<font size=-1>[ This Message was edited by: Dave C on 3/14/02 8:32am ]</font>