How far is too far? Coil location

I am doing an electronic ignition conversion on my 68 Barracuda/340.
Because of tight quarters at the rear of the engine, plus heat, I would like to mount the coil over on either the rear of the top face of the passenger fenderwell, or maybe on firewall at furthest out point, getting close to the hinge. What do u guys think ? It would mean about a 20-24 inch coil wire. Too long? I have mounted my ECM and voltage regulator under the dash, because there's no heater box, and I wanted to keep them cool
Thanks
Neal.