Which one is sitting at the Air Zoo (Kalamazoo Aviation History Museum)? What variant is it?
The Air Zoo refers to it as an SR-71B. Their image of it shows it in NASA livery as NASA 831. This was originally USAF serial number 61-7956 which was one of two SR-71's built as trainers. 61-7957 was the other and it was destroyed in a crash in 1968. They were both built as SR-71B's, not A-12's or YF-12's.
Number 956 was transferred to NASA in 1990 when the AF retired the SR-71's the first time. NASA labeled it as #831.
There is only one other dual-control trainer and it is an SR-71C, serial number 61-7981 which replaced the destroyed #956. It was made from parts of the static test model SR-71 and the aft section of YF-12A #06934.
More info at Habu.org.