8.75 Brake ???

Currently my 8.75 has the small bolt pattern, tapered axles. My plan is to buy some LBP axles with green bearings. Figuring I would only have to switch the drums to fit the larger pattern. I was informed I have to switch over the entire brake system with new backing plates, hardware and drums. Is this truely necessary? If that is the case does anyone know what it would take to switch to discs in the rear and how much more to do that? I was quoted about $350 for a drum set up.