I am making four round cakes in 10X3 pans using 6.5 cup batter for each. I will place two cakes side by side and then make the shape 3 out of the other two round cakes and place it on top of the first two cakes side by side. Hope that helps visualize. Do I need dowels? It will almost be like a cake with two layers and not another tier, so I am thinking I don't need any? I am not a professional baker. This is for my sons birthday for 50 people.

If it’s just 2 cake layers, and is under 4-5 inches tall, maybe even under 6, you shouldn’t need any dowels.

Exactly what Kitchen Siwx said  

I agree.