I have color pictures of the 870 and the 870A with a waist line and without. These pictures are both from original literature and also a picture of a pump from a collection. I doubt they were an option, and since both the 870 & the 870-A have the waist, I also doubt they are an early or late version. It appears they just made them two ways. As far as rare, I would say that all 870s are somewhat rare.
Author, 1st & 2nd editions of Gas Pump ID book, 3rd edition is now available at
www.gaspumpbible.comAir Meter ID book also available