I made a full sheet cake the I cut in half. I then torted and filled each half and would like to stack them on top of each other. Do I need to put dowels in between the two layers?
My rule of thumb is every 4 inches (give or take) I put support. I mean what you are describing sounds like it would be 4 or 5 inches tall altogether once you are finished? So no support.
If you baked off a big poppa bear sheet cake and it would be six inches or more tall when it's stacked and the fillings are heavy--I would put support.
Use your judgment. If you think it will squish into itself you won't be sorry you put support. If it's only gonna be like 4 inches tall--nah.
it will be about 7-8 inches tall.
Dowels aren't used to hold a cake together they are used to support an upper tier from crushing the tier below. With what you are describing I would treat each as a tier and have the upper half on a cake board,with dowels in the lower half supporting. You wouldn't want to have a 7 or 8 inch tall slice of cake. If it is meant to look like one tier, ice them as such but instruct the cake cutter that it is to be cut as two tiers.