Really can't say for sure but looking at the Engine Option page from the 1967 Deluxe Brochure,
shows the 360 HP 428 which appears to share the same Breather as the GP 350 HP offering.
I would think the 428 used the HD filter.
Just a guess.
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When I die, I want to go peacefully like my grandfather did, in his sleep.
Not screaming like the passengers in his car.
