A Body Disc Brake Swap 101

So I'm a little confused and I apologize in advance for my lack of experience on this subject. I completely understand the various ways to convert drum-to-disc,parts that will work and won't work, etc, but what if someone is converting SBP drum to LBP disc in the front...what happens with the rear drums? I haven't read anything regarding the swap from SBP to LBP out back.???....or have I totally missed something!! :dontknow: