Karsten Solheim followed the 69 putter series with the B69, B68, B67, and B66 putters which he advertised as "Ballnamic Putters." [And The Putter Went...PING (2017) by Jeffery B. Ellis]. First offered in 1964, the B69-B66 putters were more heel-to-toe weighted than their 69 series cousins. Karsten filed for the patent on the B69-B66 designs in January 1965, and he received the patent on January 1966. 

This Scottsdale PING B66Z Z-bend putter is in excellent condition. PING moved from Scottsdale to Phoenix in mid-1966, so this putter pre-dates that move. Therefore, Karsten only had a few months or so to produce this putter with the earliest Scottsdale address, which explains its extreme rarity.