This ROM (Hitachi HN462732) was dumped with a TL866II.
Sticker was hard to read but probably says 

33BAA
12-84

leading me to assume a datecode of dec. 1984.
Instrument: Ser.no 456-05AA4, "ACC. No. 8296"

this unit is *probably* for a 4210-4 series sensor, but I haven't been able to confirm positively.
The "signatures", artificially calculated with a tool I made (https://github.com/fenugrec/hp5004_sigtest),
do not match any of those listed in my service manual (PN 98100902 dated 8/85).

Of interesting note : the firmware appears to be some kind of Forth or indirect-threaded code implementation, and cannot easily be reverse-engineered with the usual tools (IDA, ghidra etc).

fenugrec 2020/11/30