multipilot

To build on what Rick said, you can log whatever you want in your logbook. Its your logbook and not an FAA or airline logbook. Now, that being said what the FAA will accept as flight experience is outlined in 61.51, and SIC qualifications are outlined in 61.55. Consequently, the airlines or any other FAA certified operator will want to see 61.51 time.

SIC time in a single pilot King Air operated under Part 91 will just get you a pat on the back. Personally, I would subtract that time from your overall totals when you turn in the paperwork for airlines, 8710s etc. The only other thing that "SIC" time might be good for is insurance.