Hi Clyd3,
Yes, you could make up an internal system.
But first, try to see where the phone lines ended up.
I presume they would all go back to the same place,
or most of them anyway.
My guess is an electro-mechanical unit about the size
of a household refrigerator.
Unless its very modern, then it would be chips,
and most likely gone.
If you can find this unit,
you're half way there.
If you find where it was but its gone,
you know where you stand.
In this country, such units were generally in basements.
Although they could of course be anywhere indoors.
You mention the roof space ... could the exchange unit
be in the roof ?
You say their wires are cut short,
but surely you could see where the wires went?
maybe marks in the paintwork?
maybe the old tacks or fixings ?
If you have to make it up from scratch, i would suggest
chips, unless there is a good reason why not.
Even using chips, i think that some electro-mechanical
units would be unavoidable.
If you can find the exchange unit, or even the wreckage
of it, that would be a good start.
Have a look over this page:
http://www.seg.co.uk/telecomm/automat1.htm
Regards, John