['68 K-10]

Hey everybody. I need some help with a few things. First is why would a truck have a higher hump? i have a 4 wheel drive cab with a low hump and a 2 wheel with a low hump, and i want to put the two wheel drive cab on the 4 wheel frame. i was wondering if because my 4 wheel is manual if that is why it is low because i am going to put an automatic in it. i just want to make sure the 2 wheel drive cab will work b4 i do all the work to it. also i went and bought a new crossmember for the automatic i want to put in, and it is almost exactly the same as what my manual was sitting on. for right now thats all the questions hope you guys can let me know what i need thanks
~JAKE~