You're going to need to convert to side engine mounts. With the horse shoe mount on the front and tail shaft mount in the rear, there will be nothing to keep the engine from twisting over from torque. In addition, if you're using an aluminum bell housing with a support span so far apart, there can be enough stress to cause pilot shaft/clutch alignment problems if not a broken bellhousing. You should be able to use the mounts shown on the attached link with a 1" spacer to make up for the difference in frame heights from the 62 to the later style frame.
http://67-72chevytrucks.com/vboard/s...d.php?t=369663