Assuming you are going to use "average properties", here is an example of a concentric reducer model and an eccentric reducer model.

Concentric Model:
D1 = 8.625 t1 = 0.322 L = 16.0
D2 = 6.625 t2 = 0.280

In CAESAR II -> DX = 16, Diam=7.625 Thck=.301

Eccentric Model:
D1 = 8.625 t1 = 0.322 L = 16.0
D2 = 6.625 t2 = 0.280

In CAESAR II -> DX = 16, DY=-1.00
Diam=7.625 Thck=.301