I would think you have plenty of vertical. The Taco was designed for a .25/.28. I have had both an OS .25FX and a Magnum .28 in mine and they were easily 3D capable. I have also build a twin fuselage plane and it has great performance. To a normal Taco you are add an extra fuselage and engine and a small center wing. This isn't double the weight, but you have twice the power. It's going to have tons of vertical.

If you use a computer radio, you can mix engine to rudder and have one engine cut back with rudder and should get great flat spins. Looks to me like a great project.