/6 to v8 chassis changes?

im new to these classics and have got a 71 duster im slowly picking away at. im in the process of accumulating all the parts i need for my resto... both front and rear rails, complete floor pan trans xmember... anyways, ive read that there are v8 and /6 k frames, and torsion bars? im not familiar with these what so ever. if anyone could chime in on what ill be looking at to swap out and to fit and hold the v8 under the hood thatd be great. its a non power steering car if that matters.