I thought I should document this oddity before it disappears. Currently on eBay is this 1969 model sheet and inhouse memo of Al Capp's Joe Btfsplk, World's Worst Jinx character from the "Lil' Abner" comic strip. The memo says how the title of the project (was this going to be a short? TV pilot?) has been changed from "Al Capp's Lil' Abner" to "Joe Btfsplk, World's Worst Jinx". Of course, this Warner Bros.-Seven Arts cartoon was never made. The model sheet looks very McKimson-esque to me (this same seller also has quite a bit of other original McKimson art up for bid as well, which supports the theory).
Maybe someday we'll know more about it!