Draarcy,
For summary details extracted pre-1922 from Wills (i.e. before so many were "wisped" away for ever) it is always worth having a look through the "Microfilm of original handwritten and typed records in the Public Record Office, Belfast" of the work of Tenison GROVES - a record agent who was active through the turn of the 19thC - all snapped on to 54 reels by the LDS in 1959.
For the McGOOKIN surname the relevant items from the collection look like being:
Genealogical collection of muster rolls, householders, wills, deeds, parish registers
Families Ledley-Maxwell p. 9186-9921 FHL BRITISH Film 258488
Families Montgomery-Mahoney p. 10460-11121 FHL BRITISH Film 258490
Families Mahoney-M'Ternan p. 11122-11609 FHL BRITISH Film 258491
N.B. The going can be a tad turgid, particularly thru' the handwritten pages.
Ref:
https://familysearch.org/#form=catalog[Choose ...
Search = "Author Information",
First Names = "tenison",
Last or Corporate Name = "groves".]
Not aware that any surname index of these records has ever been created.
[Quite a task!]
Capt. Jock