I've been trying out some of these old EV's lately, the 664 and also
the 636. I replaced the four pin out on these with standard XLR, since
I don't ever need to use the hi-Z output.

If you want to do this, you need to find an in-line XLR male connector
with a screw that fastens into the side of the plastic circle that has
the pins molded into it. The regular Neutrik connectors don't have
these anymore. Maybe you can take just take the part off a Neutrik and
drill your own hole, I don't know.

So open the mic up and take that four pin connector out of there. It's
a tight fit - I had to tap it out (gently!) with a hammer. Unsolder
the four wires running to the connector. You can just put some
heatshrink over the yellow wire, as that's the high impedence wire.
The red wire goes to pin 2, green to pin 3, and the orange or white
wire goes to ground, pin 1. Then put it all back together.

Note that the downside to this is that XLR cables don't lock into
place, as there's no locking tab on there.

Hope that helps,
Leigh