compact reversed cim gearbox and output shaft question

[InFlight]

An Arbor press is the "correct tool" for the job. Applying controlled steadily increased pressure until the pin slides is far better than Hammering / Pounding the pin.

An Arbor press is also handy for removing mounting pins/collars from pneumatic actuators and setting bearings in slightly undersized holes.

A one ton arbor press can be found for under $100, it really one of those basic tools that any reasonably well equipped FRC shop should have.

A drill bit is too long for the job; it's subject to column buckling with high axial force (Euler formula). You can make a short pressing tool on your lathe for a specific job. When in a hurry I have found a steel bolt the correct sizes works well enough.