If I'm not mistaken, the flop is "required" due to the "lever close" safety.
CAVEAT: Make sure your firearm is unloaded before doing these steps:
If you open the lever and look at the base of the trigger plate just behind the trigger, you'll see a little "nub" of metal sticking out a hole. Try pulling the trigger and you'll find that it won't budge --- that's the "lever close" safety preventing the firearm from discharging with an open lever. When you close the lever, it pushes that "nub" up and frees the trigger movement. With the lever open, you can press the "nub" in with the handle of a screwdriver and you'll see that you can now pull the trigger.
Here's where I think the flop comes into play... as you cycle the action, the bolt moves rearward and first moves the hammer into halfcock and then to fullcock. The movement from halfcock to fullcock occurs while the lever is open (i.e., the trigger is locked). If the trigger were one piece (i.e., the trigger shoe and sear were fixed together), the hammer would not be able to move the sear out of the way in order to fully cock since movement of the sear would require movement of the trigger and the trigger is locked by the "lever close" safety.
Hence, the two piece trigger design and its inherent "flop" which allows the sear to be moved as the hammer rotates to full cock even though the trigger shoe is immovable. The "flop" is simply the reverse situation; when the rifle is fully cocked, the sear is held by friction against the fullcock notch so forward pressure on the trigger shoe moves it forward while keeping the sear fixed.
I was puzzling over this a while back when I got my first 1953 Marlin 39a --- this rifle has a one-piece trigger so I was trying to figure out why the 336 action required a two piece trigger. That's when I realized that the 39a did not have the "lever close" safety... at least that's how I've convinced myself that the safety/two piece trigger works --- I'd love to hear what other people think.
I've never handled one of Wild West Guns "Happy Triggers" (though I'd love to as they get such great reviews), but my guess is that the trigger is still a two-piece design (as required by the Marlin's safety feature), but machined with much tighter tolerances and/or an internal spring to minimize (or apparently eliminate) forward movement of the trigger shoe when the sear is against the fullcock notch. Can anyone enlighten me on how the Happy Trigger works?
Back to the original poster, I think the "lever close" safety has always been a feature of 336's, so if you're trigger does not have flop, maybe there is a buildup of oil/grease/link that makes the trigger appear to be more resilient to the flop... best bet would be to pull the trigger plate off the rifle and take a look.
Just checked mine and the trigger has some play after the hammer is cocked. Once you press the trigger past the "slack stage", you get the normal trigger action.