Ka-Zar comics pretty much suck, but we get to see them fight an Allosaurus. That’s cool.
Reed Richards notices some bad activity in Savage Land, Thing goes to investigate, he and Ka-Zar fight the looting army.
The story (there’s really not much of one) continues directly into MTU#47, where Spider-Man and Thing fight Basilisk, and then that one goes directly into MTIO #17.
The logic of it all is nonexistent–it’s just fun to see Marvel’s two premiere done-in-one mags crossing over.