Teldorserious I looked at the current IML discs for the 90 and 200 series King Airs.
There is no listing for autofeather on 90's before LJ-362. The F-90 show it as optional equipment on all S/N's, and they all had 4 bladed props.
The 200/ B200 disc show autofeather as optional equipment all the way to the ProLine 21 equipped aircraft BB-1834 and up with a few holes in the coverage.
It may have been a mandatory option with certain props...but it was an option.
His dudeness: My boss had to add autofeather to more than a few new aircraft, the salesmen would order the aircraft without a/f and the buyer would want it. His best recollection was that it cost $30,000 USD to add it...in 1978