I wonder what the thickness of the old ring gear spacers for the type O we're compared to say other brands ? About 1/8th, 1/4 inch ? Basically the offset of a series to next ?

 

I have a spare 3.23 looks pretty thick on ring and might mill thinner to fit my 588 (3.91) diff in my Rallye as an option. If you are familiar with 12 bolt C10 truck gears the 3.73 is a 4 series unlike a Chevelle and it is a rather thin gear