Hello Ade11,
I disengaged myself here in this thread when you continued to randomly exchange components w/o previous systematic analysis / measurements.
Again, in your situation, I would also not listen to people who don't own a 3458A themselves, and evidently only disorient you further.
The 3458A requires a copper short, two references, 10V and 10kOhm, for the basic calibration.
For high frequency VAC you need an HP3325A/B generator and thermocouples of 3V, 1V and 0.5V.
Latter VAC calibration might not be needed if you don't use frequencies higher than 100kHz, or so.
The 3458a will initialize a corrupted or blank cal RAM with the default values.
These cal constants can be queried by CAL? 1,1 and CAL? 2,1: There's of course a dedicated calibration manual available, (03458-90017), better search at KEYSIGHT, they have the latest documents on their product page.
There you will also find all updated service, operation and repair manuals, and about 18 Service Notes, one of them contains information about nvRAM replacements, which might not well fit here.
I recommend to download the hp journal April 1989 which gives a lot of design background for the 3458A.
The 3458A is one of the most linear DMMs in the world, therefore it is of course no linearity calibration of the A/D required.
Being so sophisticated, it lacks any kind of power compensation of its 100:1 VDC divider, anyhow.
I also urgently recommend that you update your EPROM firmware to 8 or 9, as your old instrument, from around 1995 probably still has the old 4 or 5 versions, containing a lot of flaws.
Frank