Thanks to several people for concise answers, some humor, and offers of assistance.

What I learned - since the power for the tach comes from the instrument panel, a small wire 16 or 18 gauge, even 20 or maybe 22, will do to transmit the coil signal.  I'll probably use a bundle of 16 gauge wires so as to be ready for other projects in the future.

Hope I will get the tach wired this weekend.

Sam