Distribution/Combination/Safety Switch Block

Your info coincides with past posts. Search and you can find photos of the 2 parts (like post just before yours). I thought front disk brakes started in 1965 or earlier, not 1967 like inlinetube states. "Delay valve" sounds mis-leading since I think that function is now termed "proportioning valve". My understanding is that it decreases pressure to the rear wheel cylinders, not a timing effect.

If you don't want to be factory correct, you can get an adjustable proportioning valve for $28 (Jegs, ebay). However, I wouldn't mount it down low in the mud like the fixed factory prop valve. Smart you are adding one, since otherwise your rears can lock up first and spin you out on a turn. An adjustable one lets you dial it in for your situation (tires, engine, ...) using a wet parking lot or gravel lot and observer as you skid the tires. You want the fronts to skid first.