made the original pickups in the 1987 and 1988 540 series of guitars (540R, 540S, 540P). They have only "IBZUSA
" on them. In 89 and on, the pickups were still Dimarzio but were labeled "F1-4".
Over many threads asking about the original pups versus the later ones we've found that the F series are similar to market Dimarzio pups. For example, an F1 might be described by Dimarzio as a Tone Zone with more mid (I just made that up for illustration). Dimarzio thus points to their regular market pups for each of the F series Ibanez pups, give or take some aspect of tone.
However, those 87 and 88 pups have no Dimarzio equivalent. None. They were made by Dimarzio, for Ibanez, and they have no parallel in the Dimarzio line. They are uniquely Ibanez.
In my HH 540R I have the IBZUSA humbucker in both the bridge and neck positions. I thoroughly enjoy these pickups. I dig their sound, and I dig that that sound is not duplicated by Dimarzio since the 1988 540 series of guitars. What do you think?