I had to replace my throttle cable once when it broke on my way to work. I got home by pushing on the linkage with my finger. Made for an interesting ride! I hooked it up the carbs with a lot of cussing and needle nose pliers.
Then I read the book! I think you are supposed to unbolt the intake tubes to the heads, remove the air box and then carefully slide the carb assembly intact to the left so you can access the cable linkage easier! I'm at work right now so I can't double check but I think that's the way it is supposed to be done!
First, get as much slack as possible in the cables at the throttle grip end. Then, I slide the carbs part way out the left side, reach in with open/crescent wrenches to loosen the lock/adjuster nuts where each cable attaches at the throttle bell housing (linkage). Then, slide the adjusters/cables out of their 'mounts.' Once they are loosened, re-center the carbs and go to the right side to get the cable ends detached from where they loop onto the bell crank, with their ends slotted in the holes. It's a bit fussy, but i find that working from each side of the carbs, while pulling the whole assembly towards me a bit, really helps. Careful not to grab the actual cables with pliers, as you can damage the cable weave, leading to frayed and possibly broken cables later on. Good luck.