6 Speed Slant Six

I have the transmission fitted to the engine and under the car. I have cut the floor and torsion bar cross member out so that the transmission can go all the way up to level. I believe I now need to set the angle of the transmission and build the transmission cross member support, but how do you go about actually setting it? What do you reference from? I know the transmission and rear end angles need to correlate. I am putting a Ford 8.8 from an Explorer behind it so I was planning on setting the rear end's angle to match the transmission after it is in place, but I'm not sure how to set the transmission to start with. I'll post pictures in the next couple days.