"Annie" big haulers refers to the "10th Anniversary edition" that came out about 10 years ago..
there are now two different "generations" of Annies, both are good..
Easy way to tell if the Big Hauler in question is a more modern version, with the desirable drivetrain,
or an earlier version, with the less desirable drivetrain..
just look at the valve gear and side rods.
If they are made of metal, its good.
if they are made of plastic, its an older version, not so good.
(yes, it is true there are *some* more modern Big Haulers with the plastic rods *and* the Gen 5 drive..So its not an absolute rule,
but *in general* if you follow the "metal running gear" rule, and buy only the one with metal running gear, you will be in good shape.)
Metal valve gear, main rods and side rods:
Big Hauler with metal running gear, photo 1
Big Hauler with metal valve gear, photo 2
the metal is quite shiny, easy to tell from the plastic versions..
there are also two different styles of valve gear on the "annies"..Walschaerts and Stevenson:
Walschaerts
Stevenson
Older version, Plastic valve gear, main rods and side rods.. I would avoid these:
Big Hauler with plastic running gear.
Big Hauler with plastic running gear, photo 2.
note the the side rods are grey plastic, the difference between the metal and plastic rods is easy to distinguish in photos once you get used to seeing them.
Scot