Both were done by the same production company, FILMWAYS.

The Addams Family was done during that last 2 seasons of Mr Ed.

Barry Kelly who played Carol Post's father several times and a regular the last season.... was also a FREQUENT guest star on the Adams family.... I'd say at least 6 different times/characters. (Why not he was there everyday any how ;) )

Also one AF episode that involved a neighbor kid (I think the one Wednesday gets the crush on) , half of the Post''s living room is used for the house with different furniture.
But there is no mistaking the half curtained front window, double ranch front door and curved staircase. ;)

I read that it was the one where Morticia redecorated the neighbors' house where they used the set from Mr.Ed, but you may know better.