Taylor— the reason people collect them as part of the 68 set, even if they know them to be MB cards, is that PSA, Beckett and SCD include them as part of a master set. That’s why I have them in both of my sets. Most 1968 set collectors want them, as well as any MB collectors, hence the demand you point out that drives up the price more than that for other MB cards

We need Carlton to pop in here

Cox and Brinkman are more popular because they have been in the guides as a legit 68 Topps variation since the beginning, or close enough to it that they are considered part and parcel of the 68 Topps set.

Hot Rods are intriguing since they also show up in the salmon backed "Fun Pack" reissues that also include 67 Who Am I? (no coating) and Target: Moon. What was the purpose of that "set" originally, since Fun Packs were for overstocked and returned cards?