Yes you will need a custom front driveshaft. I am not sure of the rear driveshaft and the input gear can still be obtained from time2kill. I have not done this swap yet but it is in my near future or I would tell you what exactly to do about the shafts front and rear. Kbracing will cut and weld your crossmember for 40 bucks or so plus shipping if memory serves. Thats about all the info I have.
Oh wait, Front shaft needs to be smaller diamator and is a different length. An SS is if I remember right a shorter shaft. Don't know if a regular front shaft would work. I doubt it but I plan to try it and see once I get the cheese for a built 4l80.