Mystery Cruise Control & bad speedo cable

[SilverMiner]

Thanks in advance for any assistance, here's the deal: my speedometer doesn't work and I know it is because the cable is ruined from touching the exhaust. But I can't figure out which cable to buy to replace it.

According to my SPID, my 1980 K10 Suburban should have had the YE9 Silverado package plus the K30 Automatic Speed control (see attached pic). The YE9 part checks out, but the cruise control clearly is not factory. I can only imagine that the buyer specified cruise, but on delivery it was clear somebody goofed and the cruise was missing so the dealer installed whatever they could to make the customer happy. But definitely not a factory cruise package.

Fortunately, the previous owners had kept the info package complete so I do have the operating manual for the Cal Custom Hawk cruise control package that was installed (attached pic). What I don't know and what I wish I had was the installation instructions, because I cannot figure out how the heck the system works. It appears that the speedo cable from the transfer case (which is the one that is ruined and needs to be replaced) goes through the firewall and to the cluster, and then a separate cable comes back out to the cruise unit on the drivers fender well (see pics). I know the GM system has the cable enter the cruise unit and THEN go to the cluster. I even have an extra cable for just such a system, but it doesn't appear that it will help now.

I really, really, really don't want to have to completely dismantle my cluster to address this issue. The speedometer hasn't worked since I bought this truck, but I didn't mind because I use a GPS. But I would like to get the cruise to work again.

Does anyone have any experience or knowledge of these Cal Custom Hawk cruise control units? How does the unit on the inner fender know what the speed is? Is there some sort of goofy "Y" split in the back of the cluster? That sure seems like the hard way to do things.

And how in the heck did a Silverado get built in 1980 without cruise anyway? I thought that was integral to the YE9 package? This isn't the only SPID oddity - this Suburban also does not have the HE4 3:42 gears nor does it have the NE2 40 gal. fuel tank. Everything else seems correct, and after discovering the oddities I even double-checked the VIN vs. the title and vehicle, but it sure seems weird.