First off, Is this a GM Van Column ?? If it is, match color for color. You will have some spare wires from the column ignition. Don't worry about those.
I recommend that you pick up a column harness connector from a speed shop. Flaming River, IDIDIT , etc carries them too. $15 and it will make the conversion that much easier.
In the 64
Yellow Dark green and brown all connect to the Stop & Tail Light Harness. Dark green is the right rear directional, yellow the left. The brown is the Brake lights.
White goes to the brake light switch
Purple to Fuse panel
Dark Blue to Right Directional
Light Blue to Left Directional
Black goes to the horn relay
Just match the colors from the column to the same colors on the harness in the truck.
DVal