The reason why that set is going so high is rarity. Citrus is probably the most rare finish on Ludwigs. Then it looks cool. SO rarity drives the value up. On a Black Oyster Pearl ("Ringo" color) set, they produced many, many in that finish, but because Ringo played that color, there are many, many people who want drums in that color, in which case it isn't rarity but desirability that drives value up.
Blair, I also had a Mod Orange set (rare but not nearly as rare as Citrus Mod) that was a 12/13/16/22 set and it was a '68 model. It had the block LUDWIG on the post mount just like those do, except it was transitional in terms of the interiors: One of the drums had white painted the others were clear maple. So I am guessing by my experience that Citrus set is probably period-correct, even though it is the later clear interior it is still a post mount that is within an acceptable date range for the drums.