Did they definitely have 2 handles on that model?
I've never seen a MBH that didn't have handles on both sides of the bowl. Looking at the pics, I believe that avacado is in the same age range as the yellow one I have (early-mid '70s). Two rivets in the handle, small tab on the upper vent. I believe that the large "blemish" on the lower bowl you see in the pics is where the missing handle used to be attached. Its in the perfect spot for it if you compare the pics side by side.
Honestly, the main reason I was going to pick it up was so I could get the legs, wheels, triangle, and twist pan to put on my yellow MBH. Then I was going to try and pass the avacado bowl onto someone else who wanted it.