Problems with Challenger tracks

[Son of a gun-ner]

You say that the reinforcing frame is 25x25mm angle. From the photo the aluminum appears to be flat stock, but I wonder if I am just not seeing the angle on either side of the hull tub with flat cross pieces.

Herr Doc, if you put your hand down the front of your trousers/pants, and scratch your balls whilst squinting at the picture, you can just pick out that it's angle
Word of advice, not to be done in a public place or with company

[Herr Dr. Professor]

Those instructions are similar to the ones in the owner’s manual for my cheap Italian car.