The reproductions are up to an 1/8" or 3/16" smaller in height, and in the size of the base (both side to side and front to back). I have one of the brass and one of the aluminum bears and the aluminum is even smaller than the brass. The ears are also thicker at the top on the repro's
The bear should be 4" tall as measured from the top of the base to the top of the head, not including the ears. The base should be 2-7/16" front to back, 2-3/16" side to side at the widest point (center), and 2" at the narrowest point (extreme front or rear). These measurements can vary a bit (1/32"-1/16") depending on how much if any clean up was done to the casting. The chrome bears normally have more buffing/grinding/polishing on the edges, base, and mold line, than do the run of the mill bears. The only dates I am aware of on the bears are Jan 1949, and a very few dated 11-20-73.
The Cadets are dated Nov 1960, 11-20-73, and 9-14-74. I also have a Cadet without a date. They should be 4-29/32"+- 1/32" from the top of the base to the top of the back of his hat, the base is 2-1/8" front to back, side to side is 2-9/16" at the narrow point, 2-5/8" at the widest point.
Anything less (1/16" or more) than these measurements I would not spend my money on if I wanted only original castings. Some people don't care if it is original or a repop, they just want a bear, and if they are happy with that, and know it is a reproduction, that is fine with me. The originals can be quite pricey, specially the one holding a tractor. I have one holding a tractor that came off eBay for very little money because all the lettering and the date had been sanded off. The bear is painted black and the tractor was red. I assume the PO maybe just collected bears and did not want the IH connection (lettering) and removed it. Had they only known......