1968 GMC Speedometer Cable Help

[Willys_MB]

My truck’s speedometer has never worked. A while back I pulled the old cable out and it had broken apart and someone had removed the pieces, so all I had was a portion of it. I ordered a new cable from Rock Auto that was 38” long and it was way too short, so I measured the housing like I should have from the beginning and ordered the next size up, 63” long. That length is too long by roughly 5”. Does anybody know what length speedometer cable I need? Is this something if I go to the old guy at NAPA he can probably help me with? I’m a little confused because LMC (I know they aren’t the best) says it should be one of those two lengths, but nobody seems to have a length in between those two.

It’s a 1968 C20 with an NP435 transmission. I’m guessing the transmission is why I’m having a hard time finding the right length of speedometer cable.

Thanks in advance for any help.