Dan,
You nailed that identification and dating. The change between gray interiors and speckled occurred sometime in 1967 between Holiday serial numbers 83883 (gray) and 88308 (speckled). More examples will narrow this down more precisely.
Chill might have a little trouble finding the Top Hat "Dog Bone" double tom mount, but in the meantime, he could always put a single swivo arm in that collect. I mount a single tom arm from that position on one of my basses. The tom ends up in the same position as it would on the double mount....
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Best of luck to Chill finishing this very nice Dayton kit. The hoops need to be repainted in satin black, but other than finding the Dog Bone double mount and a Knobby for the FT, there's not much more needed.
Mike