My 67 273 has them on most of the bolts but none of the studs.
There are 7 total.
The manifolds were off the car once or twice So I can't say for sure where they should be, only that there are more than 4 (one on each stud)
FSM to the rescue...
67 sb
1 washer on each of the studs
1 washer on each of the outer most bolts (screws)
Center bolts (screws) no washer.
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