240z Wheels Cylinders- Which ones?

OK, the early 240's came with a different style wheel cylinder in the back than they had from 1972 on. For racing is there any performance or reliability difference between the two styles?? We have been using the newer style wheel cylinders, but have a number of early types that are ripe to rebuild and have as spares. Should I go through the trouble, or was there a problem with the earlier units? They are both 7/8" units, though the early style is smaller, and appears to be a bit lighter.