For the rust removal would recommend electrolysis then bead blast and finish of your choice, there are a few bits I,ve done in the restorers corner using the process, one was a scope can the other a 1903 Bayonet.

The electrolysis is is a slow process but for something like you have, it will remove all rust etc and give an idea what or if its worth continuing...... cost next to nothing need a battery charger, plastic container, some soap powder and a piece of scrap steel.