Does anyone have a Marble Cake recipe that is great for carving 3d cakes? Maybe a pound or madeira recipe. Thanks!

Last night I made a marble cake. I was experimenting and used a sour cream pound cake. It made 8 cups of batter so I took 2 cups out and added 3 squares of semi-sweet baking chocolate to that. I might could have made a little less, like 1 1/2 cups of choc. It seemed to bake just fine as far as I can tell.
My sour cream pound cake recipe:
2 sticks margarine
3 cups sugar
6 eggs
3 cups plain flour
1/2 tsp salt
1/2 tsp bak pwd
1 cup sour cream
1 tsp vanilla, 1/2 tsp almond ext, 1/2 butter flavoring

Good luck!