Cream margarine and add shortening.
Add sugar and beat until smooth.
Add egg yolks and beat well.
Combine flour and baking soda in a separate bowl. Add to cream mixture alternating with buttermilk.
Add coconut and nuts.
Fold in egg whites.
Pour into three 8" pans.
Bake at 350 degrees for 25-30 minutes. Cool and stack each cake on top of each other with a layer of icing in between each layer. Frost the top with your favorite vanilla or cream cheese icing.