I just bought an LSD Axle from Napa and it looked similar, less the center balance chunk, but would not fit into the transmission completely. It started in and then the gear teeth or main seal wouldn't clear into the last 1.5 inches of the case. So... I beat it with a sledge, thinking the clip was the issue. When I finally pulled it out again, the second brutal time; the very end of the inner spline was mutilated a bit from hitting it into the case.
It looked like the teeth were not shaved flat enough, like the stockers were. They were too sharp on the very top and that's where they got clipped going in, almost as if the diameter was slightly wrong or the teeth depth was not cut properly. It was way too cold to screw with it, in the first place.
Finally, I used parts from both the new and the old and ended up with a good axle, but what a mess. I do know the axle came from CT, and was new, not rebuilt. The triple bearing on the business end of the NAPA axle is not inter-changeable with the stock end spline. The clip ring does not fit, either. They are both larger than stock diameter and if you think you can just swap parts, you are wrong.
Try to save your original axles, if at all possible or pull them with a replacement tranny. Especially the business end, no matter what transmission you use, you want that end.