This is no doubt both mathematically and physically correct. When we construct either a proton or neutron we have “cancelled out” charge components. But what is a photon but oscillating opposite charges? Your instinct is probably correct. These charge components become trapped over their own gravity well an their propagation becomes rotation. Forward momentum is now angular momentum. $m=E/c^2$. Mass is energy in orbit which acquires through this angular momentum, inertia, mass.
