Tom, never could figure out how to attach the ebay add. Did receive the keyed handle and was in similar condition to my handles along with the decorative pattern being the same. As advertised and confirmed by your picture the narrow two sections of the shaft measured 3 1/16" we cut 5/8" off the narrowest end of the shaft drilled a hole thru the shaft attached in locking mechanism and now have 2 locking handles. The shaft on the new handle was .070"dia larger than original but did ot cause any problem in fit. We did have to drill a little wood(yes I still have the original wood frame doors) out to get the locking gizmo thru..
I think you nailed, it from what I learned the chevy suicide door handle shaft was longer as both the inside & outside handle attached to the one shaft. The pleasant surprise was the design pattern on the new handle matched my handles only difference I could see was chevy handle design may have been a little more raised. Surprising as everything else on the Buick seems to be its own style - unless my handles were from a chevy when I got the car.
Thanks for your help, Al T.