I was assuming that something of that vintage would only have been able to handle a 10BASE5 transceiver, but a wee bit of googling suggests that an UTP transceiver works well enough.

Needs a patched ROM and recompiled kernel, though! See http://www.cosam.org/computers/dec/pdp11-23/20080402.html (and the two subsequent installments)

(That cosam.org site is more what I'd be expecting for a project like this, but maybe I'm just too old and grumpy for my own good!)