yoke centering question

[mhotel1]

Hello I am running S n P motor plates and cross member with small block motor mounts for ls1/t56 setup in my 69. My question is should the transmission yoke be centered between the frame rails or off center by an inch or so? I keep hearing it both ways from people and after measureing the rear pinion yoke realizing it is offset about 1/2 inch I am totally confused as to where i should mount the trasmisson centerline. Can somebody clarify or enlighten me?

thank you
Mark