GLSNightPilot:
The S-76 horizontal tail was sized for the gross weight and CG of the A, with a maximum flight load (as dictated by its total area) just right for balancing the longitudinal axis during high G pullups. As you do a pullup and build G, the main rotor tries to take you deeper into the maneuver, and flap even more than the cyclic pitch asked for. The horizontal tail's main purpose is to develop an upload during this pullup. As the nose rotates upward, the tail is swept downward. This builds up an upload that helps cancel the main rotor's increase in nose up moment.
As the gross weight was grown from the A (10,700#) to the B (11,700#) we found that the aft CG case was only marginal in pullup stability.
I personally flew the development flights (in an A at high gross weight) that showed that the double gurney flap "tricked"the air into thinking the horizontal tail had much more chord. This extra area increased the total lift from the tail, and restored good stability.
There is somewhat more drag using the gurney flap, but it was easy, and did not require a redesign of the horizontal tail tooling (the B tail was an A tail with body filler to make it symmetrical!)
Much later, we went to a light weight new horizontal tail that was designed from scratch to be the same as the older, jury rigged one. Rather than redo all the handling qualities tests, we just made it aerodynamically the same as the original B tail.