Gareth - there are minor differences in the 1968 I sell, the 1969 Tiny sells, and more going to 1970. The 1970 car is iconic because of Donahue and Penske. I also think it looks bad to the bone!
1968 Revson car:

1970 Donahue car:

1971 Follmer car - completely different:

So, similar enough in some people's eyes...completely different in others.
Good points all though!