I used one from Hot Rod Wires on my '56. If you are planning to add air conditioning, radio, power ports, etc. that would be the way to go. You'll still be custom routing it but you'll have a harness to start with instead of having to buy all those wires.

If it's just a basic truck, I'd go with the Classic Parts one Tim mentioned. It looks like a stock harness.

"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.