The factory location for the factory washer fluid bottle is above the voltage regulator/horn relay on the drivers side of the radiator support. It is held in place by two bolts into the radiator support.
Washer Fluid Bottle Location This one is on my '65 Chevy C10, OLEBLUE. Sorry for the dirty engine bay. This picture was taken prior to the degreasing session. They are the same for '64-'66. I believe the firewall location is for the '60-'63. I hope this helps.
Tony
