Keep in mind there's a reason the Honker looks sort of familiar ... The two cars are "sisters" !
There are 5 "children" in the family . You could say there are three sisters and two brothers if we count the two cars with hard domes "males" . Starting in 1967 you get the first two . The Honker II is constructed by Alan Mann Racing and is shipped to Holman and Moody who Ford has chosen to race it . With that car we see the first family characteristics exhibited . Pay particular attention to the nose from the center of the front wheels forward , and to the rear half of the car from just aft of the roll bar . You'll see them again later . In the same time period at JWR John Wyer's crew is constructing the Ford GT40 variant known as the Mirage M1 . The outstanding feature of that design is the roughly triangular shape of the dome of the roof .
Now we move to 1968 and Alan Mann Debuts the P68 or F3L Ford prototype . It bears two of the prominent family features . If you look at it from the nose to the back of the cockpit it's basically the Honker with the Mirage roof on it ! Sure the lower lip of the radiator inlet is a little more pronounced and the whole car is a little slimmer and lower but you can't miss the look .
On to 1969 where the mostly unsuccessful P68 becomes the high-winged P69 roadster (which basically looks like an upside-down pontoon boat and other than being a bunch of curvy shapes doesn't share much with the other cars looks-wise) Meanwhile Alan Mann Racing is constructing another Can Am car for Ford and Holman Moody . Originally tested with a 377 Cu. In. Gurney Weslake engine (based on a 351 Windsor block) it got shipped to Holman Moody where it was fitted with the experimental Ford owned Magnesium 494 . The OSF retains it's family resemblance as from at least the roll bar back it retains a great resemblance to the Honker .
The point of all this description of the sequence and the similarities is to show how a man's mind gets on a track and tends to follow it as he evolves it . Over time you see the evolution and in the case of the P68 , the combination of different concepts in the cars .The reason all of these cars are a "family" is because they are successive designs from one man . Ford had a talented aerodynamicist named Len Bailey . He designed all five of these cars .