[old Chevy guy]

I'm trying to buy rear brake cables for my truck. It's a 71C20 long wheel base leaf suspension,standard 4 speed transmission,v8 350, also has a Dana rear end as opposed to the eaton. When you look up cables it lists some separate for th400 truck 39" length another list for 39 9/16 length and another for a 41" length. Why would th400 need a different cable length and why only 9/16 shorter? Seems like you could take that out on the adjustment. And so what application would need 41"? Auto zone only lists the th400 one and rock auto shows 3 but no explanation to know if I need 39 9/16 or 41. I could rip the truck apart and measure the old one I guess but then I either leave it apart for days waiting for parts to come in the mail or put it back together broken again. Hoping someone on the site has had to replace these already.