The frame and forks actually look like a Sunbeam, but definitely not with that little motor and the tank shape isn't correct for a Sunnie.
I've never seen a Guzzi or other Italian make with the down draft intake, even the little 48cc guys are all setup "standard" as it were. I don't believe any BSA's, Triumphs, or Norton's used that config either. Sure as shit 'aint a Japanese or American bike.
I have a '61 aermacchi sprint and while similar, the motors are different. The macchi motor has the cylinder slightly pointed up, like an early honda single 50 0r 90cc pushrod. All macchis had swing arm suspension. They started building bikes in the early 50's so the technology is way ahead of the bike shown.
Yeah, I think it is a guzzi 250cc grand prix bike. I recall seeing that shot, not in silloutte, somewhere.
Parks, I like your clue, Falcone, Airone, Italian for starling, etc.....all up in the air.