OK found this info

pr3-1
pr3-2
pr3-3
pr3-4

none of those are specific to an ITR head only. it could be a b16a head, could be a b17a head, could be a b16b head, could be a b18c5 or jdm b18c-r head.

pr3-[1-4] came on:

88-91 EF9 & EF8 Civic & CRX SiR
92-95 EG6/EG9 Civic SiR
92-96 EG2 USDM Del Sol VTEC (or JDM Del Sol CRX SiR)
92-93 DB2 USDM Integra GSR
96-00 EK4 & EK9 Civic SiR & Type R
96-00 DC2 & DB8 JDM Integra Type R
97-01 DC2 USDM Integra Type R
99-00 USDM Civic Si / Canadian Civic SiR