I actually have a spare rear end mount that I could modify at some point if the old girl doesn't handle well enough, thanks for the info. And just FYI, my Grandmother was born near Manchester, across the countryside from Kent!

 

While doing so certainly isn't critical for basic cruising, IMCO improving rear camber gain curves and minimizing rear toe-steer should be on the menu for any type of driving which involves spirited cornering, on or off track.

The function of lowering the inner camber strut links by the recommended 1/2" below C3 stock height (relative to the diff) is to reduce, not eliminate, excess rear negative camber gain inherent to geometry originally designed for bias ply tires. It also lowers the rear roll center, which in turn reduces rear jacking forces during cornering. While the SS bracket makes for easy adjustment, it also makes it very easy to dial out too much camber gain for non-drag racing applications. So, do adjust with caution.

To minimize adverse rear toe-steer inherent to our rear suspensions when the rear squats or rolls into bump at the outside wheel, the inner U's should be ~1/2" higher than the outer U's at static ride height. Raising the diff in the chassis per the Chevy Power book will facilitate a lower overall rear ride height with this half-shaft orientation.

Yes, both of the above specs take precedence over the "D" height given in "the book". No, I didn't come up with either of these recommendations myself (credit Mr. Greenwood for that), but having done the relative chassis maths I've become quite convinced that the above specs should be considered the default baseline settings from which the vast majority of us should strive to work when sorting out the C2/C3 IRS for anything other than drag racing.

Hope that helps.