The 8¼ is from a later car. It will bolt-in. I don't now e-brake cables will need to be juggled.
The 8¼ may be from a 73 or later disc brake car. If it is, it will have BBP wheels.
The 68 drive shaft will not fit your car unless someone has swapped out the output shaft on the transmission so that the originally installed trunion style u-joint has been replace by a cross (Spicer) type.