I looked at the episcopal wills of 1764 lonan and the death + burial dates were often identical - in one other case I have a reported death date after burial but suspect either I or the transcriber of the burial register misread a 8 as 0 or vice versa - I've come across no other julian/gregorian confusion as late as 1764 - in fact the only case I've seen was in a marriage contract where a 15 Jan 1753/4 is found but this is in Ballaugh and news of the calendar change possibly hadn't permeated to the North that year.
I've noted many clashes with reported death dates being after burials - usually by a few days - I suspect that the will you see was written sometime after burial and that memory lapse and scribal confusion were to blame.

A confusion between a 1 and a 7 is quite easy as a couple of scribes had sloping '1's with a bar at the top - however given the date has both a 1 and a 7 it should have been possible to distinguish.