The reasons why I'm not changing the story.
I will stick to the "London by night" postcard. The option would be to have a tree pub sign, but a tree he could see anywhere in London. The post card is more fun and not so obvious. It's always been an unfunny postcard that makes people think, "What's the point?". Well, here is its point. It's also a bit more obscure than the Pub Sign, which just seems too convenient ie/ an obvious story driver.
I will keep the pigeon fight scene in. The whole story is based on role reversals. The KFC tastes good then he pukes it up, the sun is warm then he gets a sunburn, London is sweet then he gets beaten up. He needs to win over something, it can't be the KFC, it can't be the sun, and it has to be something he met earlier in the story, therefore the pigeons are the only option. He has to triumph over something that earlier beat him to learn that his strengths really are prevalent at night.
He needs to win at the end of the story. He has to go home with a smile on his face, yet racing against time. Without beating the pigeons he goes to London and runs home with his tail between his legs. With the final pigeon scene he learns about his strengths as well as his failings, thus the story is worthwhile.
No one would have made 'Ferris Bueller's Day Off' if the story involved him having the idea of taking a day off, then everything went wrong, he had a rubbish day and then to top it off only just made it home in time. He has to risk everything, triumph at the end as a result of his skills (confidence for Ferris, genetic attributes for Owl), and vanquish his foe (headteacher or pigeons). Then the race home becomes a last bit of excitement to really round off the story.