How to shorten a Tach drive cable?

I need to replace the tach cable in a friends plane. The inner part is
what needs replacement. I have access to another cable but the inner
part is too long.
How can I shorten the cable? The end is square and appears to have been
put into a press to form it.

I tried to square up a piece of cable from the old one, with no success.
i attempted to pound it square with a vise and hammer.

I was looking for an old time speedo shop here in dallas to help me with
this, but I can't seem to find them any more. I guess the modern cars
have put them out of business.

Any suggestions?

Dave