Used Lectric Limited wire harnesses for the 68. Beautiful and looked like stock. I have some on the 70. On the 68, I replaced almost all the harnesses with Lectric Limited repro harnesses. I didn't replace the interior firewall harness of the 68. I'm tempted to replace the interior firewall harness on 70 since a previous wire chop job to install an aftermarket stereo and also collision damage repair is making it difficult to re-wire the interior firewall harness.
Another wire harness repro builder is M&H here in So California. They are in a community east of Bellflower CA (J&D Corvette). Last I talked to these people, Lectric Limited did not want to sell anything other than a complete harness. I think M&H will sell partial harnesses.