Don't fall for the disc rear trick. They LOOK good and generally they're easier to service, but that's about it. There's zip wrong with rear drum brakes, and the ones on the 9.5" 14 bolt are pretty big, lots of swept area. Where discs beat drums is resistance to fade, but on rear brakes, they are such a small percentage of your stopping power (30% or so) that it's not an issue. Keep them adjusted - a decent interval would be for example, at oil change time. If they're out of adjustment, your front brakes will work too hard and stopping distances will be noticeably increased.
If you want rear discs just to do it, then by all means. I'm not against them, semi-interested in it myself... Just choose your components carefully. You can easily end up with a combination that performs less than what you already have.
Richard