Searching that part number leads me to believe they may have changed the part number slightly. If you search the Trakmotive website, it still lists the GM-8026ET as the Extended Travel version of the axle for his application. https://www.trakmotive.com/wp-content/uploads/2020/03/Trakmotive-Extended-Travel-CV-Axles-3.20.pdfIt’s more than that I’m sure. The whole wrong part number basically seals the deal. Probably wrong taper to fit the output shaft and possible wrong bolt pattern.
I wouldn’t get hung up on the fact is round as I’ve put round ones in these trucks too but there are other issues the tech ran into. Main one being the wrong part number all together.
Get the right one, pop it in, roll on
That said, There isn't a lot of travel in the CV axle linearly anyway, so I don't see where that aspect is much benefit. I also don't understand the point of having the same amount of articulation on the inboard joint as you have on the outboard joint. The reason the outer joint needs more articulation is because it has to turn. If you were to max out the inner joint, the outer joint would also be at its max, and you wouldn't be able to turn. 23 degrees of articulation they advertise as the limit of the stock inner joint is more than you can get from the stock suspension anyway.