MB, don't quote me because I can't be historically absolutely sure (and here I am, a history teacher), but I think by the late 60's Speedy was fazed out and by the early 70's he was replaced by Ronald, Mayor McCheese, the Hamburgler, etc.
By the late 70's, my hometown had the second oldest remaining "original" McDonald's - it was a small structure with no indoor seating, just an interior section to come in and order take-out. But it was time to "upgrade." Because of the historical significance of our McDee's, there was a movement to preserve it while building an enjoining full-seated restaurant behind it. It went all the way up to the highest echelon who considered the preservation. It became national news (until that Steven Avery thing, but let's not talk about that), but when it would've required purchasing the homes behind it and razing them to the ground and the owners wouldn't sell, the effort ended. As the second-last original structure was torn down, the tiles from it were preserved and offered for sale with appropriate engraving on them to raise money for the planned Ronald McDonald's Houses for families of hospitalized children.
And the rest, as they say, is history.
Gerard