EIP 545A Frequency Counter Questions

I am trying to track down some information on the different
firmware versions of this counter. I own one that came without
the GPIB option. I have since found the GPIB plug in board, but
am confused in regards to the firmware. I have two manuals for
the 545, one printed around 1980 and one around 1987. There was
a change in the CPU card between these dates. The manuals also
seem to have a number of misprints or anomalies as far as the
firmware required for the GPIB opt.

Does anyone know much about these counters and have any knowledge as
to the proper firmware required for the GPIB option? Also, will the
will the newer CPU cards work in place of the older cards and vice versa??

Any information that you can provide would be appreciated.

Thanks
Jim
WB5KYE