68 barracuda wiring reverse lights and tach

Yep n yep! I downloaded all my factory schematics from there.
Have you checked the wiring diagrams in the service manual for those wires that you're missing???

Here's the link for a free download....

MyMopar - Mopar Forums & Information - Service Manuals

The a/c and transmission harnesses are sold separately, at least it was that way on my 69