Trailing Arm Lengths and my P10 project

[EVRLET]

I've been doing some research on the importance of trailing arm lengths, if there is even any importance to them. Why? I have a 1973 P10 step van and was looking at replacing the rear leaf set up. The wheelbase on a P10 is 102" and the C10 is 117.5". I can't just bolt up the C10 trailing arm set up to my P10 because it would place the trailing arm cross-member right up to the back of the transmission.

I have a bagged 67 C10 with full porterbuilt and looking at those trailing arms, I don't see why I couldn't get tubular trailing arms at a shorter length and have the cross-member right where it needs to be on my van's frame.

Does anybody know why trailing arms have to be a certain length and what potential problems may occur if I made them shorter?