the spline where the factory brake pedal slides onto, to engage the rear brake. that piece needs to be removed to bolt on mounting bracket
Oh yea, totally. take that off. I've basically removed everything stock. Besides the engine/frame and brakes.
Easy. Removing that eliminates the "reversing cam". I notice your rear brake is set up to "pull" not "push" Revive. That's because the splined cam not there any longer. If it were, you'd push down with your toe, the rod would actuate the lever forward, the cam would then pull the rear brake arm, the way it is designed. Also, without a return spring, you run the risk of the brake not releasing.
Your installation
will work, but it is not advisable nor imbued with safety measures.
I removed my spline cam too on one bike, but then had to fabricate a solution for the brake arm. I would not recommend this modification for drum brakes.