Arnold Kolb, the owner of Blackhills Aviation, told me in 1980 that he was trying to buy the Kawasaki P-2’s to covert into air tankers, but thought that there would be too many logistical issues. Blackhills morphed into Neptune Aviation after Arnold sold out.
There were also rumors at the time that various P-2 tanker operators were going to make their own P-2 turboprop conversions and get STCs for them. Besides Blackhills, I believe that Aero Union had some plans for a conversion at one time.
The Hawkins & Powers conversion plan is mentioned in our friend’s link below. Of course, H & P no longer exists, nor does Aero Union.
Anyway, here’s the link:
http://www.ruudleeuw.com/greybull-rp-may03.htm