On some trucks, such as the Gen I/Gen II S-10 and S-15, the stock driveshaft will slide into the new automatic or manual transmission. The 400/350, 700-R4, and 4L60-E transmissions all use the same spline for the transmission yoke. Depending on where the new motor is mounted, you will have to have the driveshaft lengthened or shortened, corresponding to the amount you move the engine forward or rearward. The stock rearend might be alright for your conversion, depending on how heavy your foot is. If you are going high performance, you will definitely want to look into using a larger differential. The rearend gets the same recommendation from us as the driveshaft; you should beef it up now, while the swap is in progress (Ford 9-inch rearends seem to be the differential and housings of choice).