It wouldn't be the first time someone has used a D104 in studio as an
effect.
The Silver Eagle version of the D104 has an amplifer (to work with modern
radios), so impedance is not an issue.
The mic does have a very high output (requires a 9V battery) that may easily
overload the mic input of a mixer, even with a pad engaged. There is a gain
control on the bottom of the mic.
The 4-pin connector could be wired differently depending on the radio it was
being used with, so open the connector and look at the wire colors.
The mic actually has 6 wires, including a shield.
Audio is unbalanced and between the white and shield. The other wires are
only for switching and would not be used.
Your best off with the 1/4" connector but you can try connecting the shield
to pin 1 and white to pin 2 on the XLR. (You might also have to tie pin 3 to
pin 1.)
-- Make sure phantom power is turned off if using an XLR!!! --
Switching may be quite noisy since the audio is switched "line open" so lock
the mic on, and mute the channel as needed.