Although the specific KNS-80 and KNS-81 installation manuals only specify certain King indicators as compatible, there are many different indicators that can be used with these navigation systems. The King installation manuals indicate the following nav indicators as compatible: KI-206 KNI-520 KPI-552 KPI-553 (note: the manual does list some much older indicators as well which are obsolete and unsupportable) In addition, the following indicators will interface and provide the necessary functions for VOR/LOC/GS navigation: KI-202 (VOR/LOC only) IND-350 (VOR/LOC only) IND-350A (VOR/LOC only) IND-351 IND-351A IND-351D More or less, any “non-converter” indicator should function properly with the KNS-80 and KNS-81. Please note that it is ultimately the responsibility of the installer to verify system performance, functionality, and airworthiness.