You can use my tapering instructions, except instead of a 2-inch difference from top to bottom, make it one inch. You'd taper two cakes (2 layers each), then put them together narrow end to narrow end.
Start with two same-size cake layers, say, 10-inch round.
Place a 10-inch round cake circle on one end, and an 8-inch circle on the other end. Make sure the larger, same-size board is not larger than the cake. It can be tad smaller.
Working inside a large pan or baking sheet to confine the mess, elevate the cake a few inches on something narrower than the cake, like a 6 or 7 inch cake pan.
The 8-inch board side should be up. Put non-skid mat between the cake and it's elevator so it doesn't slip off.
Now, take a long, serrated knife and, using the cake boards as guides, carve away the sides of the cake. Flip the cake over, place on it's permanent board and away you go!
If you plan to fill the layers with something other than buttercream, place a couple of small cardboard cake circles between your layers before carving.
After carving, take the two layers apart, remove the cake circles, pipe your dam, add filling and replace the layers. Trim, if necessary.
If you're going to fill with buttercream, you can do that before carving.