transmission mounting..

i put my transmission in to test fit my v-gate in the floor. put the mount in and shifter on but then the driveshaft is a few inches too long. the driveshaft and transmission are out of a 67. the car is a 68. i used the automatic transmission cross member. are they offset different? do they put different rear axles in? if they do does anyone have the measurements of the rear axle out to the yoke? i am sure its something stupid! thanks!