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The standard 8BA type clutch was the 9.5" Long with a 1"-10-spline disk drive. Long type clutch covers all have three pairs of two bolts to secure them just like the other Longs and different diameter disks have different diameter bolt pattern centers with the pairs closer together than the distance between pairs. The 59A and earlier motors used the 9 and 10-inch Long types but they have the 1 3/8"-10-spline disk drive. Pickups, police cars, and station wagons in the 8BA era used the heavier duty 10" Long clutch but they also used the heavier duty drive spline.
Borg & Beck clutches were 10" but they have six equidistant bolt holes with the next size larger bolt size. They were used on the 1949 through early 1951 8CM Mercury cars which also use the 1 3/8" 10-spline disc drive. A lot of the modern diaphragm type clutches use the old Borg & Beck bolt pattern,