1967 with disks still had a separate, adjustable proportioning valve in the rear line, located down by the frame rail. They went to the all-in-one non-adjustable unit later... I'm thinking 1970-up.
I still think that's a '66 and earlier distribution block, unless I'm just not seeing it right and it has 5 ports. '67 definitely had a dual master, which would call for a 5 port block.
