Nikon tels me that you should not use a Metz on a Nikon.

Metz told me that a 40MZ-3i with a SCA 3401 would not
work on a D70.

I used my 40MZ-3i on my Nikon D70 with a SCA 3401 M5.
And it does work.
(TTL does not work, A does work, M does work).
(Settings have to be done by hand, Iso, Aperature, Zoom)

I did compare the results with the SB800 from Nikon and I
must say that within the limited circumstances I used both,
the Metz (A) did as wel as the SB800 (full automatic iTTL).

From my correspondense with Metz :
"
The mentioned digital-camera Nikon D70s only possess of the
i-TTL-flash-control and not of the standard-TTL-flash-control anymore.
Therefore for automatic-flash-mode in connection with this camera a
flash gun with "i-TTL" will be necessary. Presently we offer for this
purpose the flash guns mecablitz 28 AF-3N, 44 AF-4iN, 54 AF-1N and 54
MZ-4iN (incl. adaptor SCA 3402 ex. version M3).
"

I did try my combination, and it worked, far better than expected.
So although some combinations are not recommended they still
can work. But do not put a flash with a high voltage connector on
a modern camera, because that can damage your camera.
My flash was low voltage so I just tried.

I am not familiar with a Metz MZ 4i.
Maybe it works completely.
Maybe only certain settings work.
Maybe it doesn't work at all.
Maybe it does damage your camera.

Good luck,
Ben Brugman