I couldn't find anything other than it's a fourth run, but I only see advertizing blurbs about the 3rd run. Thanks
What improvements are you looking for other than maybe in the price? I have one from the first Walthers run as well as one of the original LifeLikes. Both are very good engines except the LifeLike one is quite anemic in the tractive effort dept. There is no way to update the LifeLike model to the newer design with traction tires. Walthers will not sell the parts. From what I 've read on the various forums people tend to like the Walthers Y3b over the Athearn Challenger.
Other than machining the traction tire grove yourself...Ive seen it done on a lathe before, but it is not for the new machinist.