brake help please

Rear disks do little to further your actual stopping ability. A set of 10" drums, properly maintained, does just fine. On an A-body even the later 11" drums are overkill, not really worth the added weight. Keep in mind that on most cars the front/rear braking split is between 70/30 to 80/20, very little is gained even if you manage to significantly improve your stopping power. The reason new cars use them in the rear has more to do with production costs and the ability to incorporate anti lock braking features.

As far as racing goes, unless you're drag racing, I'd still skip the rear disks. All of the conversions I know about require the use of "green" bearings, which are sorely lacking when it comes to the side loads related to going around corners.