Check out Bare Knuckle Pickups from the U.K. (they ship worldwide) and in particular they have a humbucker size P90 which is called the Manhattan
and is a straight swop for a humbucker....Bare Knuckle Pickups are hand "scatterwound" and highly regarded while their Manhattan P90 is a more low output jazz P90 than a more modern high output P90 and is very oldschool and vintage sounding....also it has a rather smart somewhat art deco look
in glorious chrome very much in keeping with the Guild aesthetic.