Muffler size/dimention

[Nima]

I need to change the whole exhaust system on my truck. right now I have glass packs. Can anybody tell me what is the size/dimention (lenght,width, etc) of mufflers for our trucks? Also the inlet and outlet locations, are they centered or offseted? Can you suggest any of board vendors?
Thaks ahead.
P.S, now that I took your time, for stock engine, is there really difference between stock ram horns and headers? I am debating if I should change the whole thing. Thanks