I have two sets of KIM-1 ROMs. One set is the original KIM-1 dump by Dwight Elvey, in which the filler bytes (unused locations in the ROM) are filled with $00.
Alas the dumps by Dwight have a couple of bit errors and the NMI vector is wrong.
The other set is the result of assembling the source in which the assembler used $FF for the filler bytes. It makes sense to use $FF, since EPROMs can be programmed byte for byte ‘1’ later to ‘0’s.
Functionally the filler byte is irrelevant, so I present here the ROMs with filler byte 00 (corrected Dwight original KIM-1 dumps) and filler byte FF (assembly result).