And there are at least two William Corkills leaving wills and a decree in 1676/77. And three burials within the year [1677].
Will CORKILL ballajorey buried Maughold Jan 28 1676/77.
Will CORKILL buried Maughold Feb 22 1676/77.
Will CORKILL buried Maughold Dec 28 1677.

Wills from BL's index:
CORKIL, William 1676 b Maughold E d 0991643
CORKIL, William 1676 b Maughold E w 0991643
CORKIL, William 1676/1 Maughold A w 0106203

I am claiming this William as a possibility for Ballagorry Mooar, and assume that his is the Feb 22 1676/77 burial:
www.iomfhs.im/lawsons/LawsonBMD/twill/1676_011.html
[It was one of the transcripts which disappeared when the wills were transferred in 2008, and in the meantime Joyce transcribed it as well. Ian has combined the two versions on his website, and BOTH versions are on Jim's list with Joyce's one under 1677. She has put the Dec.1677 burial as a possibility, but that looks too late to me for a will in Book 1 1676/77. [Please note: she has "Mark" there, which was definitely Margt, not Mark.]

Joyce won't have looked at the Epis wills, but I think you looked for William Corkills there at one stage?

Sue