According to Ford documents it was late 65 production. Ether July 15 or August 15 at the engine plant if I remember correctly .
Must be August of 1965. My parents ordered a '65 Ford Ranch Wagon (Galaxie class) and I believe the schedule build date was in July of 1965. I will have to check the warrantee plate to be sure but it was a very late '65 wagon. Its 289 had the gold aircleaner and valve covers (the small diameter air cleaner).
I haven't found the sales receipts yet but I do know where the original title to the wagon is located - its issue date should be within a month of when my parents received the vehicle.