Speedbird, there rages a controversy about which side of the airframe to mount the tail rotor. A noted helicopter authority (and renowned teetotaler) Sir Nicholas of Lappos maintains that it doesn't matter as long as the tail rotor itself is stout enough.
Realize though, that a propellor can either push or pull, (see: Cessna 337) depending on which way you've aligned those vane type thingees that go 'round and 'round. Torque from the helicopter's engines will always be causing the fuselage to turn in the same direction (depending on which way the main rotor turns). In the case of the Puma, the fuselage will always desire to rotate nose-left/tail-right. Which means that the tail rotor must always produce a force to counteract that. Whether the tail rotor pulls the tail or pushes the tail matters not, really.
Some will say that a so-called "tractor" type (puller) of tail rotor is less powerful or effective than a "pusher" or vice-versa, blah blah blah. The Bell UH-1 started off with the tail rotor on one side, but evolution occured and it migrated over to the other as time went on, sort of like a flounder's eyes.
But there's more to it than that. The horizontal cyclone produced by the tail rotor interacts and is affected by the downwash from the main rotor. This interaction is different in forward flight from hovering. Obviously, hovering is where you'd like the tail rotor efficiency to be optimized, as the fuselage will more or less streamline in cruise with the help of whatever vertical fin surfaces are back there.
Engineers may find that it's not so much a case of which side of the aircraft the tail rotor is on, but which way the rotor (and its resulting airflow) rotates, like the boys at Enstrom did. It's complicated. But since the tail rotor driveshaft is always going to spin in the same direction, the easiest and cheapest way to change the direction of t/r rotation is to simply flop it over from one side of the fuselage to the other.
Clear as mud? I thought so. For an explanation more in-depth than that, you'd need to speak to an aerodynamacist. And I ain't one.