This rocket is meant to be kind of a "Rocket Scrap Yard" build. It has some Mercury, Gemini and Apollo influences. It's also a modular build. It has a removable Cargo Bay that can be installed or removed.
The upper three motor canted cluster utilizes a 24mm motor. There's a 24mm motor mount in the fin can, and the cargo bay too.
Link to Build Thread: Lakeroadster's Lifting Rocket | The Rocketry Forum