[Crist Rigotti]

I have three 20s, restored two so far. I would not reuse the speaker wires, the insulation is hardened and cracks easily. Change it.
The backelite plug needs the rivets drilled, and upon resoldering new wires NO riveting. Remove a copper rivet from the mandrel, put it through and with blunt pointed tool gently tap it to flare.

The speaker wires are pretty flexible as far as the quick examination I've done so far and in pretty good shape.  I'll do a closer look though when the time comes.  Not sure what you mean by "Remove copper rivet from mandrel," .  What copper rivet and what mandrel?