Do you still have the factory clips that were there along the bottom originally?
Do you happen to have a large body aftermarket radio installed?
Is it a full rewire, or are you just re-orienting the original wires?
Reason I ask about the radio, is that with some harnesses, the bulk is too large to travel under the radio. So keep that in mind.
Most of the original wires were either traveling along the bottom of the dash, or bundled around the steering column and cluster. But if you’re wiring from scratch, you can run some of them up along the body.